Expression of chitin synthase genes during yeast and hyphal growth phases of Candida albicans.

Chitin, the beta 1,4-linked polymer of N-acetylglucosamine, is a fibrous polysaccharide that in many yeasts helps to maintain the structure of the mother-bud junction and in filamentous fungi is often the major supporting component of the cell wall. We have previously described a Candida albicans chitin synthase, CHS1. The DNA and derived protein sequences of a second gene, CHS2, are presented and compared with previously published gene sequences. Northern blot analysis shows that strikingly different levels of synthase 1 and 2 expression occur during yeast and hyphal phases of Candida growth.

Classification of fungal chitin synthases.

Comparison of the chitin synthase genes of Saccharomyces cerevisiae CHS1 and CHS2 with the Candida albicans CHS1 gene (UDP-N-acetyl-D-glucosamine:chitin 4-beta-N-acetylglucosaminyltransferase, EC 2.4.1.16) revealed two small regions of complete amino acid sequence conservation that were used to design PCR primers. Fragments homologous to chitin synthase (approximately 600 base pairs) were amplified from the genomic DNA of 14 fungal species. These fragments were sequenced, and their deduced amino acid sequences were aligned. With the exception of S. cerevisiae CHS1, the sequences fell into three distinct classes, which could represent separate functional groups. Within each class phylogenetic analysis was performed. Although not the major purpose of the investigation, this analysis tends to confirm some relationships consistent with current taxonomic groupings.

Gene transfer mechanisms among members of the genus Rhodopseudomonas.

Recent studies on species of the genus Rhodopseudomonas, particularly R, capsulata and R. sphaeroides, have resulted in the development of a range of systems of genetic exchange without peer among the photosynthetic prokaryotes. In R. capsulata, systems of generalized transduction and R-prime formation have provided a detailed map of the arrangement of photosynthesis genes, while systems of conjugation and chromosome transfer in R, sphaeroides have provided a map of the location of genes involved in amino acid biosynthesis, antibiotic resistance and photosynthesis. A recent report of plasmid transformation in R. sphaeroides provides another important avenue for the analysis of genes such as those involved in photosynthesis and photochemical nitrogen fixation, through the application of DNA cloning technology. That plasmid transformation, generalized and specialized transduction, conjugation, chromosome transfer and R-prime formation do occur in Rhodopseudomonas indicates the rapid emergence of genetic and molecular biological techniques applicable to studies of these bacteria.

High-frequency chromosome transfer in Rhodopseudomonas sphaeroides promoted by broad-host-range plasmid RP1 carrying mercury transposon Tn501.

Insertion of the mercury resistance transposon Tn501 into broad-host-range plasmid RP1 greatly enhanced the ability of this plasmid to promote chromosome transfer in the photosynthetic bacterium Rhodopseudomonas sphaeroides. Compared with the wild-type RP1, which produced less than 10(-8) recombinants per donor cell, RP1::Tn501 produced between 10(-3) and 10(-7) recombinants per donor cell depending upon the marker selected. Plasmid RP1::Tn501 promoted polarized transfer of the chromosome from one or perhaps two origins on the chromosome, giving rise to two linkage groups. All of the biosynthetic and antibiotic resistance genes that have been mapped, including those involved in photosynthesis, occur on one or another of these linkage groups.