Tripartite Regulation of the glpFKD Operon Involved in Glycerol Catabolism by GylR, Crp, and SigF in Mycobacterium smegmatis.

The glpD (MSMEG_6761) gene encoding glycerol-3-phosphate dehydrogenase was shown to be crucial for M. smegmatis to utilize glycerol as the sole carbon source. The glpD gene likely forms the glpFKD operon together with glpF and glpK, encoding a glycerol facilitator and glycerol kinase, respectively. The gylR (MSMEG_6757) gene, whose product belongs to the IclR family of transcriptional regulators, was identified 182 bp upstream of glpF It was demonstrated that GylR serves as a transcriptional activator and is involved in the induction of glpFKD expression in the presence of glycerol. Three GylR-binding sites with the consensus sequence (GKTCGRC-N3-GYCGAMC) were identified in the upstream region of glpF by DNase I footprinting analysis. The presence of glycerol-3-phosphate was shown to decrease the binding affinity of GylR to the glpF upstream region with changes in the quaternary structure of GylR from tetramer to dimer. Besides GylR, cAMP receptor protein (Crp) and an alternative sigma factor, SigF, are also implicated in the regulation of glpFKD expression. Crp functions as a repressor, while SigF induces expression of glpFKD under energy-limiting conditions. In conclusion, we suggest here that the glpFKD operon is under the tripartite control of GylR, SigF, and Crp, which enables M. smegmatis to integrate the availability of glycerol, cellular energy state, and cellular levels of cAMP to exquisitely control expression of the glpFKD operon involved in glycerol metabolism.IMPORTANCE Using genetic approaches, we first revealed that glycerol is catabolized through the glycolytic pathway after conversion to dihydroxyacetone phosphate in two sequential reactions catalyzed by glycerol kinase (GlpK) and flavin adenine dinucleotide (FAD)-containing glycerol-3-phosphate dehydrogenase (GlpD) in M. smegmatis Our study also revealed that in addition to the GylR transcriptional activator that mediates the induction of the glpFKD operon by glycerol, the operon is regulated by SigF and Crp, which reflect the cellular energy state and cAMP level, respectively.

SPR analysis of promoter binding of Synechocystis PCC6803 transcription factors NtcA and CRP suggests cross-talk and sheds light on regulation by effector molecules.

Surface plasmon resonance monitoring of the binding of transcription factors cAMP receptor protein (CRP) and nitrogen control factor of cyanobacteria (NtcA) from Synechocystis sp. PCC6803 to promoter fragments of glnA, glnN (NtcA regulon) and cccS (CRP regulon), revealed exclusive CRP binding to cccS, whereas NtcA was bound to all three promoters with different affinities, which were strongly increased by the NtcA activator 2-oxoglutarate. Effective NtcA affinity for 2-oxoglutarate varied with the promoter. High-affinity promoters and the NtcA-coactivating protein PII-interacting protein X (PipX) increased NtcA affinity towards 2-oxoglutarate, suggesting PipX-stabilization of the 2-oxoglutarate-bound NtcA conformation. PipX binding to NtcA required 2-oxoglutarate and was much tighter (Kd≈85 nM) than to the PipX-sequestering PII protein. NtcA appears to require more strongly PipX and 2-oxoglutarate (2OG) for estimulating gene expression at promoters having "imperfect" NtcA binding sites.

Enhancing E. coli tolerance towards oxidative stress via engineering its global regulator cAMP receptor protein (CRP).

Oxidative damage to microbial hosts often occurs under stressful conditions during bioprocessing. Classical strain engineering approaches are usually both time-consuming and labor intensive. Here, we aim to improve E. coli performance under oxidative stress via engineering its global regulator cAMP receptor protein (CRP), which can directly or indirectly regulate redox-sensing regulators SoxR and OxyR, and other ~400 genes in E. coli. Error-prone PCR technique was employed to introduce modifications to CRP, and three mutants (OM1~OM3) were identified with improved tolerance via H(2)O(2) enrichment selection. The best mutant OM3 could grow in 12 mM H(2)O(2) with the growth rate of 0.6 h(-1), whereas the growth of wild type was completely inhibited at this H(2)O(2) concentration. OM3 also elicited enhanced thermotolerance at 48°C as well as resistance against cumene hydroperoxide. The investigation about intracellular reactive oxygen species (ROS), which determines cell viability, indicated that the accumulation of ROS in OM3 was always lower than in WT with or without H(2)O(2) treatment. Genome-wide DNA microarray analysis has shown not only CRP-regulated genes have demonstrated great transcriptional level changes (up to 8.9-fold), but also RpoS- and OxyR-regulated genes (up to 7.7-fold). qRT-PCR data and enzyme activity assay suggested that catalase (katE) could be a major antioxidant enzyme in OM3 instead of alkyl hydroperoxide reductase or superoxide dismutase. To our knowledge, this is the first work on improving E. coli oxidative stress resistance by reframing its transcription machinery through its native global regulator. The positive outcome of this approach may suggest that engineering CRP can be successfully implemented as an efficient strain engineering alternative for E. coli.

[Advances in mechanism of Escherichia coli carbon catabolite repression].

Bacteria often sequentially utilize coexisting carbohydrates in environment and firstly select the one (frequently glucose) easiest to metabolize. This phenomenon is known as carbon catabolite repression (CCR). In existing Chinese teaching materials of molecular biology and related courses, unclear or even wrong interpretations are given about CCR mechanism. A large number of studies have shown that rather than the existence of intracellular glucose, CCR is mainly caused by the glucose transport process coupling with glucose phosphorylation via the phosphoenolpyruvate: carbohydrate phosphotransferase system PTS. The transport process leads to accumulation of dephosphorylated form of EAGlc.This form of EAGlc can bind the membrane-localized LacY protein to block the uptake of lactose inducer. cAMP functions in activation of key genes involved in PTS system to strengthen the role of inducer exclusion. In addition, dephosphorylated form of EBGlc and Yee bind global transcription repressor Mlc to ensure the expression of key genes involved in the PTS system. This review summarizes the current advancement in mechanism of Escherichia coli carbon catabolite repression.

Hypoxia-inducible factor-2alpha is a catabolic regulator of osteoarthritic cartilage destruction.

Osteoarthritic cartilage destruction is caused by an imbalance between anabolic and catabolic factors. Here, we show that hypoxia-inducible factor-2alpha (HIF-2alpha, encoded by EPAS1) is a catabolic transcription factor in the osteoarthritic process. HIF-2alpha directly induces the expression in chondrocytes of genes encoding catabolic factors, including matrix metalloproteinases (MMP1, MMP3, MMP9, MMP12 and MMP13), aggrecanase-1 (ADAMTS4), nitric oxide synthase-2 (NOS2) and prostaglandin-endoperoxide synthase-2 (PTGS2). HIF-2alpha expression was markedly increased in human and mouse osteoarthritic cartilage, and its ectopic expression triggered articular cartilage destruction in mice and rabbits. Moreover, mice transgenic for Epas1 only in chondrocytes showed spontaneous cartilage destruction, whereas heterozygous genetic deletion of Epas1 in mice suppressed cartilage destruction caused by destabilization of the medial meniscus (DMM) or collagenase injection, with concomitant modulation of catabolic factors. Our results collectively demonstrate that HIF-2alpha causes cartilage destruction by regulating crucial catabolic genes.

Clp and RpfF up-regulate transcription of pelA1 gene encoding the major pectate lyase in Xanthomonas campestris pv. campestris.

Exopolysaccharide and several extracellular enzymes of Xanthomonas campestris pv. campestris (Xcc), the causative agent of black rot in crucifers, are virulence determinants. In this study, two Xcc annotated extracellular pectate lyase genes, pelA1 and pelA2, belonging to family 1 of the polysaccharide lyase, were characterized. Sequence and mutational analyses have demonstrated that pelA1 encodes the major pectate lyase, whereas pelA2 is not transcribed. Using the 5' RACE method, the pelA1 transcription initiation site was mapped at nucleotide G, 103 nt upstream of the pelA1 start codon. Promoter analysis demonstrated that polygalacturonic acid and CaCl(2) induce the expression of pelA1. Transcriptional fusion assays also indicated that Clp (cAMP receptor protein-like protein) and RpfF (an enoyl-CoA hydratase homologue that is required for the synthesis of cis-11-methyl-2-dodecenoic acid, a low molecular weight diffusible signal factor, DSF) positively regulate pelA1 transcription. Gel retardation assays showed that Clp exerts a positive control over expression of pelA1 by direct binding to the upstream Clp-binding site. In conclusion, the present research demonstrated that pelA1 codes for the major pectate lyase in Xcc strain Xc17 and that its expression is up-regulated by Clp and RpfF. This is the first study to characterize pectate lyase gene expression in Xcc.

Downregulation of the Escherichia coli guaB promoter by upstream-bound cyclic AMP receptor protein.

The Escherichia coli guaB promoter (P(guaB)) is responsible for directing transcription of the guaB and guaA genes, which specify the biosynthesis of the nucleotide GMP. P(guaB) is subject to growth rate-dependent control (GRDC) and possesses an UP element that is required for this regulation. In addition, P(guaB) contains a discriminator, three binding sites for the nucleoid-associated protein FIS, and putative binding sites for the regulatory proteins DnaA, PurR, and cyclic AMP receptor protein (CRP). Here we show that the CRP-cyclic AMP (cAMP) complex binds to a site located over 100 bp upstream of the guaB transcription start site, where it serves to downregulate P(guaB). The CRP-mediated repression of P(guaB) activity increases in media that support lower growth rates. Inactivation of the crp or cyaA gene or ablation/translocation of the CRP site relieves repression by CRP and results in a loss of GRDC of P(guaB). Thus, GRDC of P(guaB) involves a progressive increase in CRP-mediated repression of the promoter as the growth rate decreases. Our results also suggest that the CRP-cAMP complex does not direct GRDC at P(guaB) and that at least one other regulatory factor is required for conferring GRDC on this promoter. However, PurR and DnaA are not required for this regulatory mechanism.

Role of Vfr in regulating exotoxin A production by Pseudomonas aeruginosa.

Pseudomonas aeruginosa exotoxin A (ETA) production depends on the virulence-factor regulator Vfr. Recent evidence indicates that the P. aeruginosa iron-starvation sigma factor PvdS also enhances ETA production through the ETA-regulatory gene regA. Mutants defective in vfr, regA and pvdS, plasmids that overexpress these genes individually and lacZ transcriptional/translational fusion plasmids were utilized to examine the relationship between vfr, regA and pvdS in regulating P. aeruginosa ETA production. ETA concentration and regA expression were reduced significantly in PAODeltavfr, but pvdS expression was not affected. Overexpression of Vfr produced a limited increase in ETA production in PAODeltapvdS, but not PAODeltaregA. Additionally, overexpression of either RegA or PvdS did not enhance ETA production in PAODeltavfr. RT-PCR analysis showed that iron did not affect the accumulation of vfr mRNA in PAO1. These results suggest that: (i) Vfr enhances toxA expression in PAO1 both directly and indirectly through regA, but not through pvdS; (ii) vfr expression is not regulated by iron; and (iii) both Vfr and PvdS cooperate in the presence of RegA to achieve a maximum level of toxA expression.

Regulation of expression of the tricarballylate utilization operon (tcuABC) of Salmonella enterica.

The tricarballylate utilization locus (tcuRABC) of Salmonella enterica serovar Typhimurium is comprised of a 3-gene operon (tcuABC) that encodes functions that allow this bacterium to use tricarballylate as a source of carbon and energy, and the tcuR gene, which encodes a putative LysR-type transcriptional regulator. In our studies, transcription of the tcuABC operon peaked at mid-log phase, and declined moderately during stationary phase. This pattern was not due to a change in the amount of TcuR in the cell, as tcuR expression did not change under the conditions tested, and TcuR did not control tcuR expression. Tricarballylate was the co-inducer. tcuABC expression was negatively affected by the cAMP receptor protein (Crp). Expression of tcuABC was one order of magnitude higher in a crp mutant strain than in the crp(+) strain; derepression of tcuABC expression was also observed in a strain lacking adenylate cyclase (Cya). At present, it is unclear whether the effect of Crp is direct or indirect. Studies with molecular mimics of tricarballylate showed that the co-inducer site restricts binding of structural mimics that contain a hydroxyl group. Two classes of TcuR constitutive variants were isolated. Class I variants responded to tricarballylate, while Class II did not.

Functional roles of arcA, etrA, cyclic AMP (cAMP)-cAMP receptor protein, and cya in the arsenate respiration pathway in Shewanella sp. strain ANA-3.

Microbial arsenate respiration can enhance arsenic release from arsenic-bearing minerals--a process that can cause arsenic contamination of water. In Shewanella sp. strain ANA-3, the arsenate respiration genes (arrAB) are induced under anaerobic conditions with arsenate and arsenite. Here we report how genes that encode anaerobic regulator (arcA and etrA [fnr homolog]) and carbon catabolite repression (crp and cya) proteins affect arsenate respiration in ANA-3. Transcription of arcA, etrA, and crp in ANA-3 was similar in cells grown on arsenate and cells grown under aerobic conditions. ANA-3 strains lacking arcA and etrA showed minor to moderate growth defects, respectively, with arsenate. However, crp was essential for growth on arsenate. In contrast to the wild-type strain, arrA was not induced in the crp mutant in cultures shifted from aerobic to anaerobic conditions containing arsenate. This indicated that cyclic AMP (cAMP)-cyclic AMP receptor (CRP) activates arr operon transcription. Computation analysis for genome-wide CRP binding motifs identified a putative binding motif within the arr promoter region. This was verified by electrophoretic mobility shift assays with cAMP-CRP and several DNA probes. Lastly, four putative adenylate cyclase (cya) genes were identified in the genome. One particular cya-like gene was differentially expressed under aerobic versus arsenate respiration conditions. Moreover, a double mutant lacking two of the cya-like genes could not grow with arsenate as a terminal electron acceptor; exogenous cAMP could complement growth of the double cya mutant. It is concluded that the components of the carbon catabolite repression system are essential to regulating arsenate respiratory reduction in Shewanella sp. strain ANA-3.

Direct transcriptional control of the plasminogen activator gene of Yersinia pestis by the cyclic AMP receptor protein.

Horizontal gene transfer events followed by proper regulatory integration of a gene drive rapid evolution of bacterial pathogens. A key event in the evolution of the highly virulent plague bacterium Yersinia pestis was the acquisition of plasmid pPCP1, which carries the plasminogen activator gene, pla. This promoted the bubonic form of the disease by increasing bacterial dissemination from flea bite sites and incidentally enhanced replication in respiratory airways during pneumonic infection. We determined that expression of pla is controlled by the global regulator cyclic AMP (cAMP) receptor protein (Crp). This transcription factor is well conserved among distantly related bacteria, where it acts as a soluble receptor for the ubiquitous signaling molecule cAMP and controls a global network of metabolic and stress-protective genes. Crp has a similar physiological role in Y. pestis since loss of its function resulted in an inability to metabolize a variety of nonglucose substrates. Activation of pla expression requires a transcription activation element of the pla promoter that serves as a Crp binding site. Crp interaction with this site was demonstrated to occur only in the presence of cAMP. Alteration of the Crp binding site nucleotide sequence prevented in vitro formation of Crp-DNA complexes and inhibited in vivo expression of pla. The placement of pla under direct regulatory control of Crp highlights how highly adapted pathogens integrate laterally acquired genes to coordinate virulence factor expression with global gene networks to maintain homeostasis through the infectious life cycle.

The cyclic AMP receptor protein modulates colonial morphology in Vibrio cholerae.

Inactivation of the quorum-sensing regulator HapR causes Vibrio cholerae El Tor biotype strain C7258 to adopt a rugose colonial morphology that correlates with enhanced biofilm formation. V. cholerae mutants lacking the cyclic AMP (cAMP) receptor protein (CRP) produce very little HapR, which results in elevated expression of Vibrio exopolysaccharide (vps) genes and biofilm compared to the wild type. However, Deltacrp mutants still exhibited smooth colonial morphology and expressed reduced levels of vps genes compared to isogenic hapR mutants. In this study we demonstrate that deletion of crp and cya (adenylate cyclase) converts a rugose DeltahapR mutant to a smooth one. The smooth DeltahapR Deltacrp and DeltahapR Deltacya double mutants could be converted back to rugose by complementation with crp and cya, respectively. CRP was found to enhance the expression of VpsR, a strong activator of vps expression, but to diminish transcription of VpsT. Ectopic expression of VpsR in smooth DeltahapR Deltacrp and DeltahapR Deltacya double mutants restored rugose colonial morphology. Lowering intracellular cAMP levels in a DeltahapR mutant by the addition of glucose diminished VpsR expression and colonial rugosity. On the basis of our results, we propose a model for the regulatory input of CRP on exopolysaccharide biosynthesis.

Regulation of sialic acid transport and catabolism in Haemophilus influenzae.

Virulence of nontypeable Haemophilus influenzae (NTHi) is dependent on the decoration of lipooligosaccharide with sialic acid. This sugar must be derived from the host, as NTHi cannot synthesize sialic acids. NTHi can also use sialic acid as a carbon source. The genes encoding the sialic acid transporter and the genes encoding the catabolic activities are localized to two divergently transcribed operons, the siaPT operon and the nan operon respectively. In this study, we identified SiaR as a repressor of sialic acid transport and catabolism in NTHi. Inactivation of siaR resulted in the unregulated expression of the genes in both operons. Unregulated catabolism of sialic acid in the siaR mutant resulted in the reduction of surface sialylation and an increase in serum sensitivity. In addition to SiaR-mediated repression, CRP, the cAMP receptor protein, was shown to activate expression of the siaPT operon but not the nan operon. We describe a model in which SiaR and CRP work to modulate intracellular sialic acid levels. Our results demonstrate the importance of SiaR-mediated regulation to balance the requirement of surface sialylation and the toxic accumulation of intracellular sialic acid.

The multiple roles of CRP at the complex acs promoter depend on activation region 2 and IHF.

acs encodes a high-affinity enzyme that permits survival during carbon starvation. As befits a survival gene, its transcription is subject to complex regulation. Previously, we reported that cAMP receptor protein (CRP) activates acs transcription by binding tandem DNA sites located upstream of the major acsP2 promoter and that the nucleoid protein IHF (integration host factor) binds three specific sites located just upstream. In vivo, the sequence that includes these IHF sites exerts a positive effect on CRP-dependent transcription, while a construct containing only the most proximal site exhibits reduced transcription compared with the full-length promoter or with a construct lacking all three IHF sites. Here, we defined the minimal system required for this IHF-dependent inhibition, showing it requires the promoter-distal CRP site and an amino acid residue located within activation region 2 (AR2), a surface determinant of CRP that interacts with RNA polymerase (RNAP). Surprisingly, for a Class III promoter, disruption of AR2 caused significant changes in the activity and structure of both the full-length promoter and the construct with the single proximal IHF site. We propose that AR2, together with IHF, mediates formation of a multi-protein complex, in which RNAP is stabilized in an open complex that remains poised on the promoter ready to respond rapidly to environmental changes.

New targets for the cyclic AMP receptor protein in the Escherichia coli K-12 genome.

Recent genomic studies with Escherichia coli K-12 have suggested scores of previously unexplored targets for the cyclic AMP receptor protein (CRP) global transcription regulator. Eleven of these loci were cloned and CRP binding was demonstrated at eight of these targets. It is shown that CRP can activate transcription at five of these targets and the functional DNA sites for CRP are identified. It is reported that CRP functions as a Class I activator at the aer promoter and as a Class II activator at the gatY, sdaC, ychH and malX promoters.

Expression of Escherichia coli DcuS-R two-component regulatory system is regulated by the secondary internal promoter which is activated by CRP-cAMP.

The DcuS-R two-component system of Escherichia coli senses C4-dicarboxylates of the medium and regulates expression of the genes related to utilization of them. It is known that phospho-DcuR induces expression of genes such as the dcuB-fumB operon, the frdABCD operon, and the dctA gene. We analyzed promoters of the dcuS-R operon to elucidate the transcriptional regulation system. We found a novel internal promoter within the dcuS gene that is regulated by the transcriptional regulator, CRP-cAMP, in both aerobic and anaerobic conditions.

Identification of regulatory network topological units coordinating the genome-wide transcriptional response to glucose in Escherichia coli.

BACKGROUND: Glucose is the preferred carbon and energy source for Escherichia coli. A complex regulatory network coordinates gene expression, transport and enzyme activities in response to the presence of this sugar. To determine the extent of the cellular response to glucose, we applied an approach combining global transcriptome and regulatory network analyses. RESULTS: Transcriptome data from isogenic wild type and crp- strains grown in Luria-Bertani medium (LB) or LB + 4 g/L glucose (LB+G) were analyzed to identify differentially transcribed genes. We detected 180 and 200 genes displaying increased and reduced relative transcript levels in the presence of glucose, respectively. The observed expression pattern in LB was consistent with a gluconeogenic metabolic state including active transport and interconversion of small molecules and macromolecules, induction of protease-encoding genes and a partial heat shock response. In LB+G, catabolic repression was detected for transport and metabolic interconversion activities. We also detected an increased capacity for de novo synthesis of nucleotides, amino acids and proteins. Cluster analysis of a subset of genes revealed that CRP mediates catabolite repression for most of the genes displaying reduced transcript levels in LB+G, whereas Fis participates in the upregulation of genes under this condition. An analysis of the regulatory network, in terms of topological functional units, revealed 8 interconnected modules which again exposed the importance of Fis and CRP as directly responsible for the coordinated response of the cell. This effect was also seen with other not extensively connected transcription factors such as FruR and PdhR, which showed a consistent response considering media composition. CONCLUSION: This work allowed the identification of eight interconnected regulatory network modules that includes CRP, Fis and other transcriptional factors that respond directly or indirectly to the presence of glucose. In most cases, each of these modules includes genes encoding physiologically related functions, thus indicating a connection between regulatory network topology and related cellular functions involved in nutrient sensing and metabolism.

Effects of crp deletion in Salmonella enterica serotype Gallinarum.

BACKGROUND: Salmonella enterica serotype Gallinarum (S. Gallinarum) remains an important pathogen of poultry, especially in developing countries. There is a need to develop effective and safe vaccines. In the current study, the effect of crp deletion was investigated with respect to virulence and biochemical properties and the possible use of a deletion mutant as vaccine candidate was preliminarily tested. METHODS: Mutants were constructed in S. Gallinarum by P22 transduction from Salmonella Typhimurium (S. Typhimurium) with deletion of the crp gene. The effect was characterized by measuring biochemical properties and by testing of invasion in a chicken loop model and by challenge of six-day-old chickens. Further, birds were immunized with the deleted strain and challenged with the wild type isolate. RESULTS: The crp deletions caused complete attenuation of S. Gallinarum. This was shown by ileal loop experiments not to be due to significantly reduced invasion. Strains with such deletions may have vaccine potential, since oral inoculatoin with S. Gallinarum Deltacrp completely protected against challenge with the same dose of wild type S. Gallinarum ten days post immunization. Interestingly, the mutations did not cause the same biochemical and growth changes to the two biotypes of S. Gallinarum. All biochemical effects but not virulence could be complemented by providing an intact crp-gene from S. Typhimurium on the plasmid pSD110. CONCLUSION: Transduction of a Tn10 disrupted crp gene from S. Typhimurium caused attenuation in S. Gallinarum and mutated strains are possible candidates for live vaccines against fowl typhoid.

A C-helix residue, Arg-123, has important roles in both the active and inactive forms of the cAMP receptor protein.

The cAMP receptor protein (CRP) of Escherichia coli exists in an equilibrium between active and inactive forms, and the effector, cAMP, shifts that equilibrium to the active form, thereby allowing DNA binding. For this equilibrium shift, a C-helix repositioning around the C-helix residues Thr-127 and Ser-128 has been reported as a critical local event along with proper beta4/beta5 positioning. Here we show that another C-helix residue, Arg-123, has a unique role in cAMP-dependent CRP activation in two different ways. First, Arg-123 is important for proper cAMP affinity, although it is not critical for the conformational change with saturating amounts of cAMP. Second, Arg-123 is optimal for stabilizing the inactive conformation of CRP when cAMP is absent, thereby allowing a maximal range of regulation by cAMP. However, Arg-123 does not appear to be critical for a functional response to cAMP, as has been proposed previously (Berman, H. M., Ten Eyck, L. F., Goodsell, D. S., Haste, N. M., Korney, A., and Taylor, S. S. (2005) Proc. Natl. Acad. Sci. U. S. A. 102, 45-50). Based on mutagenic evidence, we also propose the basis for the stabilization of the inactive form to be through a salt interaction between Asp-68 and Arg-123.

Phototaxis and impaired motility in adenylyl cyclase and cyclase receptor protein mutants of Synechocystis sp. strain PCC 6803.

We have carefully characterized and reexamined the motility and phototactic responses of Synechocystis sp. adenylyl cyclase (Cya1) and catabolite activator protein (SYCRP1) mutants to different light regimens, glucose, 3-(3,4-dichlorophenyl)-1,1-dimethylurea, and cyclic AMP. We find that contrary to earlier reports, cya1 and sycrp1 mutants are motile and phototactic but are impaired in one particular phase of phototaxis in comparison with wild-type Synechocystis sp.