Versatility of global transcriptional regulators in alpha-Proteobacteria: from essential cell cycle control to ancillary functions

Abstract

Recent data indicate that cell cycle transcription in many alpha-Proteobacteria is executed by at least three conserved functional modules in which pairs of antagonistic regulators act jointly, rather than in isolation, to control transcription in S-, G2- or G1-phase. Inactivation of module components often results in pleiotropic defects, ranging from cell death and impaired cell division to fairly benign deficiencies in motility. Expression of module components can follow systemic (cell cycle) or external (nutritional/cell density) cues and may be implemented by auto-regulation, ancillary regulators or other (unknown) mechanisms. Here, we highlight the recent progress in understanding the molecular events and the genetic relationships of the module components in environmental, pathogenic and/or symbiotic alpha-proteobacterial genera. Additionally, we take advantage of the recent genome-wide transcriptional analyses performed in the model alpha-Proteobacterium Caulobacter crescentus to illustrate the complexity of the interactions of the global regulators at selected cell cycle-regulated promoters and we detail the consequences of (mis-)expression when the regulators are absent. This review thus provides the first detailed mechanistic framework for understanding orthologous operational principles acting on cell cycle-regulated promoters in other alpha-Proteobacteria.

Short-Stalked Prosthecomicrobium hirschii Cells Have a Caulobacter-Like Cell Cycle

“…The P. hirschii genome contains orthologs of the global regulators GcrA, CcrM, SciP, and CtrA. In C. crescentus, these global regulators function in regulatory modules to control progression through the cell cycle: the CtrA/MucR, GcrA/CcrM, and CtrA/SciP modules regulate sequential transcription of target genes during the G 1 , S, and G 2 phases, respectively (8,52). The P. hirschii genome also contains orthologs of proteins predicted to regulate CtrA function, including CckA, ChpT, DivL, and DivK.…”

“…Bioinformatic analysis of alphaproteobacterial genomes suggests that the core architecture of the regulatory genes that govern Caulobacter cell cycle progression is broadly conserved within at least two clades of Alphaproteobacteria, Rhizobiales and Caulobacterales (7,8). Furthermore, genes shown to be essential for cell cycle progression in C. crescentus have also been shown to have important functions in cell cycle regulation of Agrobacterium tumefaciens (9)(10)(11)(12), Sinorhizobium meliloti (3,(13)(14)(15)(16), and Brucella abortus (14,(17)(18)(19)(20).…”

Essential Genome of the Metabolically Versatile Alphaproteobacterium Rhodopseudomonas palustris

“…For example, the RPA0595 protein is 52% identical to the BioC biotin biosynthesis protein in C. crescentus (CCNA_00874), while RPA1263 shares 75% identity with SciP (CCNA_00948), a protein that represses the transcription of genes activated by the master cell cycle regulator CtrA. RPA1626 is homologous to ChpT, a histidine phosphotransferase which controls the activity of CtrA (42,43).…”

The (unusual) aspartic acid in the metal coordination sphere of the prokaryotic zinc finger domain

“…This protein differs from the eukaryotic counterpart: its globular structure centred around a zinc ion consists of 58 amino acids (from Pro9 to Tyr66) arranged in a βββαα topology and stabilized by an extensive hydrophobic core (15 amino acid residues) [24]. Ros is the first structurally described member of a large family of bacterial proteins that have interesting and fundamental roles in the bacterial cell life [12,[25][26][27][28][29][30][31][32]. Interestingly, Ros homologues present several amino acid substitutions in the positions occupied by zinc-binding residues in Ros and despite these amino acids changes, these proteins maintain the ability to specifically bind the DNA [12,33].…”