ABSTRACT
Two Escherichia coli genes, expressed from multicopy plasmids, are shown to cause partial induction of prophage lambda in recA mutant lysogens. One is rcsA, which specifies a positive transcriptional regulator of the cps genes, which are involved in capsular polysaccharide synthesis. The other is dsrA, which specifies an 85-nucleotide RNA that relieves repression of the rcsA gene by histone-like protein H-NS. Genetic contexts known to increase Cps expression also cause RecA-independent lambda induction: the rcsC137 mutation, which causes constitutive Cps expression, and the lon and rcsA3 mutations, which stabilize RcsA. Lambdoid phages 21, phi80, and 434 are also induced by RcsA and DsrA overexpression in recA lysogens. Excess lambda cI repressor specifically blocks lambda induction, suggesting that induction involves repressor inactivation rather than repressor bypass. RcsA-mediated induction requires RcsB, the known effector of the cps operon, whereas DsrA-mediated induction is RcsB independent in stationary phase, pointing to the existence of yet another RecA-independent pathway of prophage induction.
Subject(s)
Bacteriophage lambda/growth & development , Bacteriophage lambda/genetics , DNA-Binding Proteins , Escherichia coli Proteins , Escherichia coli/genetics , Escherichia coli/virology , Genes, Bacterial , Rec A Recombinases/genetics , Virus Activation/genetics , Bacterial Proteins/biosynthesis , Bacterial Proteins/genetics , Coliphages/genetics , Coliphages/growth & development , DNA, Bacterial/genetics , Escherichia coli/metabolism , Gene Library , Models, Biological , Mutation , Phenotype , Plasmids/genetics , Repressor Proteins/biosynthesis , Repressor Proteins/genetics , Viral Proteins , Viral Regulatory and Accessory ProteinsABSTRACT
Escherichia coli K-12 lytic phage C1 was earlier isolated in our laboratory. Its adsorption is controlled by at least three bacterial genes: dcrA, dcrB, and btuB. Our results provide evidence that the dcrA gene located at 60 min on the E. coli genetic map is identical to the sdaC gene. This gene product is an inner membrane protein recently identified as a putative specific serine transporter. The dcrB gene, located at 76.5 min, encodes a 20-kDa processed periplasmic protein, as determined by maxicell analysis, and corresponds to a recently determined open reading frame with a previously unknown function. The btuB gene product is known to be an outer membrane receptor protein responsible for adsorption of BF23 phage and vitamin B12 uptake. According to our data the DcrA and DcrB proteins are not involved in these processes. However, the DcrA protein probably participates in some cell division steps.