Bacteria precisely coordinate DNA replication and chromosome segregation with cell division; accurate regulation of each of these processes is critical to genome inheritance and thus reproductive success. During fast growth, Bacillus subtilis carries out multi-fork replication and maintains multiple partial copies of the genome. However, during the developmental process of sporulation, B. subtilis shuts down DNA replication initiation and maintains only two copies of the chromosome. SirA (Sporulation inhibitor of replication A), is a protein produced only during sporulation that has been shown to inhibit new rounds of DNA replication by interacting directly with the initiator protein DnaA. Apart from inhibiting replication, I discovered that SirA acts in the same pathway as Soj to facilitate capture of the origin of segregation (oriC) in the forespore compartment during sporulation. I identified residues in both SirA and DnaA that are important for mediating the SirA-DnaA interaction and demonstrate that the two functions of SirA (replication inhibition and oriC segregation) are genetically separable. My data support the model that SirA interacts with DnaA Domain I to inhibit DNA replication initiation and with DnaA Domain III to promote oriC segregation.
