期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2008
卷号：105
期号：30
页码：10577-10582
DOI：10.1073/pnas.0803904105
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Vibrio cholerae, the agent of cholera, has two circular chromosomes. In bacteria that contain a single chromosome, initiation of chromosome DNA replication is mediated by DnaA, a AAA+ ATPase that unwinds the origin of replication. There is little knowledge regarding initiation of chromosome replication in bacteria with more than one chromosome. Here, we purified V. cholerae DnaA and RctB, which have been implicated in the replication of V. cholerae chromosome II, and characterized their activities in vitro. We found that RctB has origin-specific unwinding activity and can melt the origin of chromosome II (oriCIIvc) but not the origin of chromosome I (oriCIvc); conversely, DnaA promoted the unwinding of oriCIvc and not oriCIIvc. The activity of DnaA and several plasmid initiator proteins is stimulated by ATP binding. We found that RctB bound and hydrolyzed ATP even though RctB lacks any apparent ATP-binding motifs. However, we unexpectedly found that ATP inhibited the oriCIIvc binding activity of RctB, suggesting that the ATP-bound form of RctB cannot initiate replication of chromosome II. Supporting this idea, we identified an RctB mutant that does not bind ATP and found that expression of this ATP-blind RctB mutant in V. cholerae leads to significant overinitiation of chromosome II and marked inhibition of V. cholerae growth. These observations suggest that the rules that license the replication of the two V. cholerae chromosomes differ.
关键词：initiation of replication ; RctB ; DnaA ; cell cycle
