A developmentally regulated chromosomal origin of replication uses essential transcription elements.

Abstract

Only one of the two chromosomes in the asymmetric Caulobacter predivisional cell initiates replication in the progeny cells. Transcription from a strong promoter within the origin occurs uniquely from the replication-competent chromosome at the stalked pole of the predivisional cell. This regulated promoter has an unusual sequence organization, and transcription from this promoter is essential for regulated {cell type-specific) replication. Our analysis defines a new class of bacterial origins and suggests a coupling between transcription and replication that is consistent with the phylogenetic relationship of Caulobacter to the ancestral mitochondrion.

New members of the ctrA regulon: the major chemotaxis operon in Caulobacter is CtrA dependent

“…No similarity to the consensus k35 sequence for biosynthetic promoters was observed (Malakooti et al, 1995). A putative CtrA-binding site was detected, but only 5 out of 9 residues matched the proposed consensus sequence, TTAA-N ( -TTAAC (Marczynski et al, 1995 ;Quon et al, 1996). Neither half-site was completely conserved with the consensus motif.…”

“…This two-component response regulator acts in either a positive or negative regulatory manner to activate or repress expression of several genes involved in flagellar biogenesis, chromosome replication (Marczynski et al, 1995) and lipopolysaccharide production (Leclerc et al, 1998). Since cagA and mcpA expression is not abolished in class II flagellar mutants we determined whether ctrA The ctrA xylose-conditional strain (MRKA520) harbouring reporter plasmids pCS141 (mcpA-lacZ), pRCH04 (cagA-lacZ), pCS44 (filL-lacZ), pWZ162 (fliQ-lacZ) or pCS139 (tacp-lacZ) was grown to OD '!!…”

Regulation of the Caulobacter flagellar gene hierarchy; not just for motility

“…The DNA sequence motif recognized by CtrA is also conserved in the essential DNA methylase gene ccrM (Stephens et al, 1995) and hemE, whose transcription near the chromosome origin coincides with the initiation of DNA replication (Marczynski et al, 1995). Mutational analysis of CtrA indicates that its activity is regulated by phosphorylation (Quon et al, 1996).…”

Functional importance of RNA interactions in selection of translation initiation codons

“…As more and more transcription start sites are mapped, it is apparent that an increasing number of prokaryotic mRNAs have no functional SD signal due to very short or absent 5Ј untranslated leader regions (Bibb et al, 1994;Marczynski et al, 1995;Wu and Janssen, 1996, and references therein). Among them, many leaderless transcripts of actinomycete genes encode essential proteins that confer antibiotic resistance on bacterial cells (Bibb et al, 1994).…”

“…Some of these leaderless mRNAs carry sequences with complementarity to the putative ADB region of Streptomyces 16S rRNA (Bibb et al, 1994;Wu and Janssen, 1996) or conserved decoding centre of Caulobacter crescentus 16S rRNA (Marczynski et al, 1995). However, the functional importance of these postulated downstream recognition signals and/or influence of potential trans-acting protein factors (with possible S1-like functions) for translation of leaderless mRNAs in these bacterial groups remains to be experimentally proven.…”