CELL-CYCLE REGULATION AND CELL-TYPE-SPECIFIC LOCALIZATION OF THE FTSZDIVISION INITIATION PROTEIN IN CAULOBACTER

Many genes involved in cell division and DNA replication and their pro tein products hare been identified in bacteria; however, little is kno wn about the cell cycle regulation of the intracellular concentration of these proteins, It has been shown that tile level of the tubulin-li ke GTPase FtsZ is critical for the initiation of cell division in bact eria, We show that the concentration of FtsZ varies dramatically durin g the cell cycle of Caulobacter crescentus, Caulobacter produce two di fferent tell types at each cell division: (i) a sessile stalked fell t hat can initiate DNA replication immediately after cell division and ( ii) a motile swarmer cell in which DNA replication is blocked, After c ell division, only the stalked cell contains FtsZ. FtsZ is synthesized slightly before the swarmer cells differentiate into stalked cells an d the intra-cellular concentration of FtsZ is maximal at the beginning of cell division, Late in the cell cycle, after the completion of chr omosome replication, the level of FtsZ decreases dramatically . This d ecrease is probably mostly due to the degradation of FtsZ in the swarm er compartment of the predivisional cell, Thus, the variation of FtsZ concentration parallels the pattern of DNA synthesis. Constitutive exp ression of FtsZ leads to defects in stalk biosynthesis suggesting a ro le for FtsZ in this developmental process in addition to its role in c ell division.