Tau-mediated coupling between Pol III synthesis and DnaB helicase unwinding helps maintain genomic stability.

The τ-subunit of the clamp loader complex physically interacts with both the DnaB helicase and the polymerase III (Pol III) core α-subunit through domains IV and V, respectively. This interaction is proposed to help maintain rapid and efficient DNA synthesis rates with high genomic fidelity and plasticity, facilitating enzymatic coupling within the replisome. To test this hypothesis, CRISPR-Cas9 editing was used to create site-directed genomic mutations within the dnaX gene at the C terminus of τ predicted to interact with the α-subunit of Pol III.

Dysregulated DnaB unwinding induces replisome decoupling and daughter strand gaps that are countered by RecA polymerization.

The replicative helicase, DnaB, is a central component of the replisome and unwinds duplex DNA coupled with immediate template-dependent DNA synthesis by the polymerase, Pol III. The rate of helicase unwinding is dynamically regulated through structural transitions in the DnaB hexamer between dilated and constricted states. Site-specific mutations in DnaB enforce a faster more constricted conformation that dysregulates unwinding dynamics, causing replisome decoupling that generates excess ssDNA and induces severe cellular stress.