| الوصف: |
Genome stability of Escherichia coli critically depends on the combined action of proteins involved in DNA replication, repair and recombination. In the first chapter, we discover that removal of LexA, a transcriptional repressor of the SOS response, and ClpXP protease leads to novel cell division phenotypes. These phenotypes are largely due to RecN upregulation. RecN belongs to the Structural Maintenance of Chromosomes family of proteins and plays a role in the sister chromatid cohesion during Double-Strand Break Repair (DSBR). We believe that the cell division phenotypes may mimic a late stage of the SOS response when RecN is at its highest level and further delays cell division by holding together regions of the chromosomes and inhibiting the Z-ring formation. RecN is thought to physically interact with RecA recombinase essential for DSBR and induction of the SOS response. The second chapter explores a function of the recA(Q300R) mutant, which is phenotypically similar to ∆recN and where the RecN/RecA interaction is hypothesized to be eliminated. An epistasis analysis between a chromosomal recA(Q300R) mutant and ∆recN in the wild-type and recBC sbcBC backgrounds reveals that a double mutant has an additive phenotype when compared to either single mutant. These data suggest that recA(Q300R) and ∆recN remove functions in genetically distinct pathways for the phenotypes tested. Thus, they question importance of RecA Q300 for the RecN/RecA interaction in vivo. The last chapter investigates a vital role of PriA and PriC in recruiting the replication machinery when replication fork collapses. Studies done in vitro suggest that PriA and PriC associate with the C-terminus of single-stranded DNA-binding protein (SSB) to gain access to the broken replication fork. We test in vivo the disruptive potential of missense mutations within the SSB-binding pocket of PriA and PriC. A priC351(R155A) mutation completely abolishes the gene function supporting previous data and demonstrating significance of the PriC/SSB interaction. In contrast, priA341(R697A), priA344(R697E) and priA345(Q701E) mutations have no effect. They do, however, display negative phenotypes in a priB null strain, which are partially suppressed by SSB overproduction. These studies give further insights into the orchestration of reactions needed for the replication restart. |
