Regulation of C. crescentus cell cycle and methylation of the chromosome.
(A) Schematic of the C. crescentus cell cycle and the regulatory interactions that control G1-phase promoters. Transcription from G1-phase promoters is activated by phosphorylated CtrA (CtrA~P, in blue) and repressed by MucR1/2. CtrA~P accumulates in pre-divisional and swarmer (SW) cells, and is eliminated by regulated proteolysis in the stalked (ST) cell upon compartmentalization and at the swarmer to stalked cell differentiation. The red bar indicates that MucR1/2 proteins are present at all stages of the cell cycle. (B) Schematic of the chromosome replication and adenine methylation (m6A) during the C. crescentus cell cycle. Chromosome replication and methylation are shown for the same cell cycle stages depicted in panel A. In non-replicative SW cells (T10) the chromosome is methylated on both strands. Upon differentiation into ST cells (T40), chromosome replication start from the origin (blue star) located at the old cell pole; progression of the replisomes (orange dots) generates hemi-methylated chromosomes (black and green lines represent respectively the methylated and unmethylated strand; T70 and T100). The cell cycle-regulated adenine methyltransferase CcrM is synthesized only in late pre-divisional cells, where it methylates the newly synthesized chromosome strands. CcrM is then specifically proteolyzed by the Lon protease. The purple numbers indicate the position along the chromosome of the P169 (1), P1149 (2) and P2901 (3) promoters. T10, T40, T70 and T100 indicate the time after synchronization at which the samples for anti-MucR1 ChIP-Exo were taken (see text).