Mycobacterium tuberculosis oriC sequestration by MtrA response regulator.

The regulators of Mycobacterium tuberculosis DNA replication are largely unknown. Here, we demonstrate that in synchronously replicating M. tuberculosis, MtrA access to origin of replication (oriC) is enriched in the post-replication (D) period. The increased oriC binding results from elevated MtrA phosphorylation (MtrA∼P) as evidenced by reduced expression of dnaN, dnaA and increased expression of select cell division targets. Overproduction of gain-of-function MtrAY102C advanced the MtrA oriC access to the C period, reduced dnaA and dnaN expression, interfered with replication synchrony and compromised cell division. Overproduction of wild-type (MtrA+) or phosphorylation-defective MtrAD56N did not promote oriC access in the C period, nor affected cell cycle progression. MtrA interacts with DnaA signaling a possibility that DnaA helps load MtrA on oriC. Therefore, oriC sequestration by MtrA∼P in the D period may normally serve to prevent untimely initiations and that DnaA-MtrA interactions may facilitate regulated oriC replication. Finally, despite the near sequence identity of MtrA in M. smegmatis and M. tuberculosis, the M. smegmatis oriC is not MtrA-target. We conclude that M. tuberculosis oriC has evolved to be regulated by MtrA and that cell cycle progression in this organisms are governed, at least in part, by oscillations in the MtrA∼P levels.