A PARI fehérje szerepe a rekombináció-függő folyamatok szabályozásában elakadt replikációs villa esetén

The replication stalled due to DNA damage can be rescued via several mechanisms. The choice of activating a certain pathway is strictly regulated; it is important whether a fast but mutagenic translesion synthesis should take place in the cell or template switching, which is error free but goes through complicated secondary structures. The role of the molecular switch between these pathways is fulfilled by the PCNA protein and its posttranslational modifications. Its ubiquitination activates the DNA damage tolerance pathways, while its SUMOylation inhibits recombination-dependent processes. In this latter, as demonstrated in yeast cells, the Srs2 protein is an important player. Moreover, inhibition of recombination is achieved at several levels. Srs2, with its helicase activity, participates in the disassembly of the D-loops and, in a SUMOylated PCNA-dependent manner, it inhibits the extension of the D-loops. In human cells, all these functions are shared by several proteins, with PARI having been shown to interact with PCNA. During our studies, we revealed the molecular mechanism via which PARI inhibits homologous recombination at the stalled replication fork: by inhibiting D-loop extension, PARI prevents duplication from a homologous region for a long period thus decreasing the chance of crossovers, inhibiting further recombination events, and possible genome rearrangements

Opposing Roles of FANCJ and HLTF Protect Forks and Restrain Replication during Stress

The DNA helicase FANCJ is mutated in hereditary breast and ovarian cancer and Fanconi anemia (FA). Nevertheless, how loss of FANCJ translates to disease pathogenesis remains unclear. We addressed this question by analyzing proteins associated with replication forks in cells with or without FANCJ. We demonstrate that FANCJ-knockout (FANCJ-KO) cells have alterations in the replisome that are consistent with enhanced replication stress, including an aberrant accumulation of the fork remodeling factor helicase-like transcription factor (HLTF). Correspondingly, HLTF contributes to fork degradation in FANCJ-KO cells. Unexpectedly, the unrestrained DNA synthesis that characterizes HLTF-deficient cells is FANCJ dependent and correlates with S1 nuclease sensitivity and fork degradation. These results suggest that FANCJ and HLTF promote replication fork integrity, in part by counteracting each other to keep fork remodeling and elongation in check. Indicating one protein compensates for loss of the other, loss of both HLTF and FANCJ causes a more severe replication stress response