Initiation of chromosomal replication is similar in eubacteria, eukaryotes, and archaea. In general, initiation takes place only once per cell cycle, although in rapidly dividing cells in some bacterial families, a new round can begin before the ongoing round has finished. Justine Collier of the University of Lausanne, Switzerland, and Lucy Shapiro of Stanford University find a new regulatory pathway that controls timing and frequency of chromosomal replication in the alpha-proteobacterium Caulobacter crescentus. "We found that initiation is restricted to only once per cell cycle, and to a specific period in the cell cycle, thanks to the action of an essential protein that we named HdaA," says Collier. "This new pathway is critical, since it ensures that each daughter cell will inherit only  one chromosome after cell division." The researchers also find that HdaA is conserved in many bacterial species but not in eukaryotes, suggesting, says Collier, that "HdaA could make an interesting target for new antibacterials that might be harmless to humans. We are now searching for new pieces [of the puzzle of cell cycle regulaton] and trying to connect them with the others," says Collier. "Our ultimate goal is to understand how the cell cycle regulatory system works in bacteria."

(J. Collier and L. Shapiro. 2009. Feedback control of DnaA-mediated replication initiation by replisome-associated HdaA protein in Caulobacter. J. Bacteriol. 191:5706-5716.)