Asymmetric expression of the gyrase B gene from the replication-competent chromosome in the Caulobacter crescentus predivisional cell.

The bacterium Caulobacter crescentus undergoes an asymmetric cell division resulting in the formation of two different daughter cells, a motile swarmer cell and a nonmotile stalked cell. These two cell types differ in their program of gene expression, their ability to replicate DNA, and the physical properties of their nucleoids. We show here that two genes, gyrB (encoding the gyrase B subunit) and orf-1, are specifically transcribed from the chromosome in the portion of the predivisional cell destined for the progeny stalked cell. This is in contrast to a subset of flagellar genes which are transcribed from the chromosome in the incipient swarmer portion of the predivisional cell. gyrB and orf-1 are within a newly identified cluster of genes involved in DNA replication and recombination, including dnaN and recF. The transcription of gyrB and orf1 occurs from the replication-competent chromosome in stalked and predivisional cells and is silenced in swarmer cells. We hypothesize that selective silencing of groups of genes in the chromosomes at the swarmer and stalked poles of the predivisional cell results in the different developmental programs and the difference in replicative ability of the two progeny cells.