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 divi sion resulting in the formation of two different daughter cells, a mot ile swarmer cell and a nonmotile stalked cell. These two cell types di ffer in their program of gene expression, their ability to replicate D NA, and the physical properties of their nucleoids. We show here that two genes, gyrB (encoding the gyrase B subunit) and orf-1, are specifi cally transcribed from the chromosome in the portion of the predivisio nal 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 r eplication and recombination, including dnaN and recF. The transcripti on of gyrB and orf1 occurs from the replication-competent chromosome i n stalked and predivisional cells and is silenced in swarmer cells. We hypothesize that selective silencing of groups of genes in the chromo somes at the swarmer and stalked poles of the predivisional cell resul ts in the different developmental programs and the difference in repli cative ability of the two progeny cells.