Role of core promoter sequences in the mechanism of swarmer cell-specific silencing of gyrB transcription in Caulobacter crescentus

• Main Authors: Gober James W, England Jennifer C
• Format: Article
• Language: English
• Published: BMC 2005-05-01
• Series: BMC Microbiology
• Online Access: http://www.biomedcentral.com/1471-2180/5/25

<p>Abstract</p> <p>Background</p> <p>Each <it>Caulobacter crescentus </it>cell division yields two distinct cell types: a flagellated swarmer cell and a non-motile stalked cell. The swarmer cell is further distinguished from the stalked cell by an inability to reinitiate DNA replication, by the physical properties of its nucleoid, and its discrete program of gene expression. Specifically, with regard to the latter feature, many of the genes involved in DNA replication are not transcribed in swarmer cells.</p> <p>Results</p> <p>We show that for one of these genes involved in DNA replication, <it>gyrB</it>, its pattern of temporal expression depends upon an 80 base pair promoter region with strong resemblance to the <it>Caulobacter crescentus </it>σ⁷³consensus promoter sequence; regulation does not appear to be affected by the general strength of the promoter activity, as mutations that increased its conformity with the consensus did not affect its cell-cycle expression pattern. Transcription from the <it>gyrB </it>promoter <it>in vitro </it>required only the presence of the σ⁷³RNA polymerase (from <it>E. coli</it>) and the requisite nucleoside triphosphates, although a distinct binding activity, present in crude whole-cell extracts, formed a complex <it>gyrB </it>promoter DNA. We also assayed the effect on <it>gyrB </it>expression in strains containing mutations in either <it>smc </it>or <it>dps</it>, two genes encoding proteins that condense DNA. However we found there was no change in the temporal pattern of <it>gyrB </it>transcription in strains containing deletions in either of these genes.</p> <p>Conclusion</p> <p>These experiments demonstrate that <it>gyrB </it>transcription does not require any auxiliary factors, suggesting that temporal regulation is not dependent upon an activator protein. Swarmer-specific silencing may not be attributable to the observed physical difference in the swarmer cell nucleoid, since mutations in either <it>smc </it>or <it>dps</it>, two genes encoding proteins that condense DNA, did not alter the temporal pattern of <it>gyrB </it>transcription in strains containing deletions in either of these genes. Rather a repressor that specifically recognizes sequences in the <it>gyrB </it>promoter region that are also probably essential for transcription, is likely to be responsible for controlling cell cycle expression.</p>