Cell cycle regulator phosphorylation stimulates two distinct modes of binding at a chromosome replication origin

In Caulobacter crescentus, the global response regulator CtrA controls chromosome replication and determines the fate of two different cell progenies. Previous studies proposed that CtrA represses replication by binding to five sites, designated [a–e], in the replication origin. We show that phosphorylated CtrA binds sites [a–e] with 35- to 100–fold lower K(d) values than unphosphorylated CtrA. CtrA phosphorylation stimulates two distinct modes of binding to the replication origin. Phosphorylation stimulates weak intrinsic protein–protein cooperation between half-sites and does not stimulate CtrA–P binding unless protein–DNA contacts are made at both half-sites. CtrA phosphorylation also stimulates cooperative binding between complete sites [a] and [b]. However, binding to each of the other CtrA-binding sites [c], [d] and [e] is completely independent and suggests a modular organization of replication control by CtrA. We therefore propose a model where a phosphorelay targets separate biochemical activities inside the replication origin through both cooperative and independent CtrA-binding sites

Selective cell cycle transcription requires membrane synthesis in Caulobacter

Caulobacter crescentus divides asymmetrically and creates distinct polar membrane surfaces that partition during the cell cycle to distinct cell progeny. Blocking membrane synthesis prevented transcription from selective promoters involved in asymmetric cell division. Transcription from sigma-54-dependent flagellar promoters was blocked completely; however, transcription from the CtrA response regulator-dependent flagellar promoters was activated but reduced. Transcription from the ccrM (DNA methylation) promoter and the che (chemosensory) promoter was also blocked completely. Transcription from a strong promoter at the chromosome replication origin was first stopped then induced by blocked membrane synthesis. We propose a feedback control coupling membrane synthesis to transcription that selectively supports membrane-associated processes such as flagellar assembly, chemosensory biogenesis and chromosome replication

N6-methyl-adenine: an epigenetic signal for DNA-protein interactions.

International audienceN(6)-methyl-adenine is found in the genomes of bacteria, archaea, protists and fungi. Most bacterial DNA adenine methyltransferases are part of restriction-modification systems. Certain groups of Proteobacteria also harbour solitary DNA adenine methyltransferases that provide signals for DNA-protein interactions. In gamma-proteobacteria, Dam methylation regulates chromosome replication, nucleoid segregation, DNA repair, transposition of insertion elements and transcription of specific genes. In Salmonella, Haemophilus, Yersinia and Vibrio species and in pathogenic Escherichia coli, Dam methylation is required for virulence. In alpha-proteobacteria, CcrM methylation regulates the cell cycle in Caulobacter, Rhizobium and Agrobacterium, and has a role in Brucella abortus infection