Fig. 7.

Model of the distinct control of active CcrM in progeny cells following an asymmetric cell division. CcrM transcription and translation are confined to the predivisional cell, methylating GANTC sites on both hemimethylated daughter chromosomes (13, 14). Cell division generates 2 types of progeny cells: a motile swarmer cell and a sessile stalked cell. In swarmer cells, CcrM is completely proteolyzed by Lon, which is stimulated on a DNA-based platform, so by the time it differentiates into a stalked cell and DNA replication is initiated, CcrM is cleared from the cell. In progeny stalked cells, however, immediate chromosomal replication does not provide adequate time for proteolysis of remaining CcrM inherited from the predivisional cells. Instead of clearance by protein degradation, CcrM is sequestered to the new cell pole away from the chromosome, concurrent with the immediate initiation of chromosome replication. Sequestered CcrM has minimum contact with chromosome DNA and Lon, therefore preventing remethylation of newly synthesized chromosomal DNA. The fully methylated chromosome is indicated by a solid red line, and the hemimethylated chromosome is indicated by a dashed red line.