Chromosomal Replication Initiation Machinery of Low-G+C-Content Firmicutes

Much of our knowledge of the initiation of DNA replication comes from studies in the Gram-negative model organismEscherichia coli . However, the location and structure of the origin of replication within theE. coli genome and the identification and study of the proteins which constitute theE. coli initiation complex suggest that it might not be as universal as once thought. The archetypal low-G+C-content Gram-positiveFirmicutes initiate DNA replication via a unique primosomal machinery, quite distinct from that seen inE. coli , and an examination oforiC in theFirmicutes speciesBacillus subtilis indicates that it might provide a better model for the ancestral bacterial origin of replication. Therefore, the study of replication initiation in organisms other thanE. coli , such asB. subtilis , will greatly advance our knowledge and understanding of these processes as a whole. In this minireview, we highlight the structure-function relationships of theFirmicutes primosomal proteins, discuss the significance of theiroriC architecture, and present a model for replication initiation atoriC .