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

Abstract

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-J, 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-l are within a newly identified cluster of genes involved in DNA replication and recombination, including dnaN and recF. The transcription of gyrB and orfi occurs from the replicationcompetent 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.

Cell cycle progression inCaulobacterrequires a nucleoid-associated protein with high AT sequence recognition

“…Two separate lines of evidence support the possibility that the swarmer and stalked cell types of Caulobacter exhibit distinct nucleoid compaction or higher-order nucleoid structures. First, the nucleoids of swarmer and stalked cells exhibit markedly different sedimentation rates and contain distinct complements of associated protein (8,(52)(53)(54). Second, because the chromosome fills the cytoplasmic space in both daughter compartments (16), the swarmer nucleoid must be packaged into only ∼70% the volume afforded to that of the stalked cell nucleoid.…”

“…1). Each morphotype expresses a unique complement of genes that encode cell type-specific functions (e.g., motility, chemotaxis, encapsulation, or chromosome replication), the regulation of which can be attributed, at least in part, to an ensemble of interdependent, spatiotemporally restricted global transcriptional regulators that are organized into a highly robust control circuit (7)(8)(9)(10)(11)(12)(13)(14)(15). However, the control of more than 40% of cell cycle-regulated promoters cannot be accounted for by these master regulators (14), implying the existence of additional regulatory proteins that influence development through interaction(s) with the Caulobacter genome.…”

An alkB gene homolog is differentially transcribed during the Caulobacter crescentus cell cycle

“…Transcription decreases to basal levels again in predivisional cells. This pattern of transcription is similar to that of many genes involved in DNA replication and to the temporal pattern of DNA synthesis in Caulobacter (13,23,24). The difference in the levels of alkB gene transcription between swarmer and stalked cells, however, is not established in predivisional cells, as observed for gyrB and orf-1 (24), but rather takes place only upon cell division.…”

“…The events that lead to this selectivity are not known. However, the expression of many genes required for DNA replication either does not occur or occurs at low levels in swarmer cells and occurs at high levels in stalked cells (13,(23)(24)(25). The differential expression of these genes has been suggested to be one of the mechanisms responsible for the DNA synthetic cycle in Caulobacter (23,24).…”

“…However, the expression of many genes required for DNA replication either does not occur or occurs at low levels in swarmer cells and occurs at high levels in stalked cells (13,(23)(24)(25). The differential expression of these genes has been suggested to be one of the mechanisms responsible for the DNA synthetic cycle in Caulobacter (23,24).In this report we describe the identification of the C. crescentus alkB gene and its expression in the presence of alkylating agents and throughout the cell cycle of the bacterium. The alkB gene in C. crescentus was found in a clone which was previously reported to contain the heat shock genes dnaK and dnaJ (13); the gene was located upstream of dnaK and was transcribed in the opposite orientation.…”