A consensus promoter sequence for Caulobacter crescentus genes involved in biosynthetic and housekeeping functions

Caulobacter crescentus differentiates prior to each cell division to form two different daughter cells: a monoflagellated swarmer cell and a nonmotile stalked cell. Thus, one might expect that developmentally expressed genes would be regulated by mechanisms different from those used to regulate the expression of the biosynthetic genes. To determine a consensus promoter sequence for genes involved in biosynthetic or housekeeping functions, DNA fragments containing the regulatory regions of the ilvD, ilvR, cysC, pleC, and fdxA genes were cloned. S1 nuclease protection mapping and primer extension techniques were used to identify the transcription initiation sites. Comparison of the regulatory regions of these genes with those of the published sequences of the ilvBN, rrnA, trpFBA, dnaA, dnaK, hemE, and rsaA genes has resulted in the identification of a putative promoter consensus sequence. The -35 region contains the sequence TTGACGS, which is similar to the Escherichia coli -35 region, while the -10 region, GCTANAWC, has a more balanced GC content than the corresponding region in E. coli. Oligonucleotide-directed site-specific mutagenesis of both the ilvBN and pleC promoters indicates that mutations that make a promoter more like the consensus result in increased promoter activity, while mutations decreasing similarity to the consensus result in decreased promoter activity.