The G157C Mutation in the Escherichia Coli Sliding Clamp Specifically Affects Initiation of Replication.
Johnsen, L., Flaatten, I., Morigen, Dalhus, B., Bjoras, M., Waldminghaus, T., Skarstad, K.(2011) Mol Microbiol 79: 433
- PubMed: 21219462 
- DOI: https://doi.org/10.1111/j.1365-2958.2010.07453.x
- Primary Citation of Related Structures:  
2XUR - PubMed Abstract: 
Escherichia coli cells with a point mutation in the dnaN gene causing the amino acid change Gly157 to Cys, were found to underinitiate replication and grow with a reduced origin and DNA concentration. The mutant β clamp also caused excessive conversion of ATP-DnaA to ADP-DnaA. The DnaA protein was, however, not the element limiting initiation of replication. Overproduction of DnaA protein, which in wild-type cells leads to over-replication, had no effect in the dnaN(G157C) mutant. Origins already opened by DnaA seemed to remain open for a prolonged period, with a stage of initiation involving β clamp loading, presumably limiting the initiation process. The existence of opened origins led to a moderate SOS response. Lagging strand synthesis, which also requires loading of the β clamp, was apparently unaffected. The result indicates that some aspects of β clamp activity are specific to the origin. It is possible that the origin specific activities of β contribute to regulation of initiation frequency.
Organizational Affiliation: 
Department of Cell Biology, Institute for Cancer Research, The Norwegian Radium Hospital, Oslo University Hospital, Oslo, Norway.