Functions Of Flap Endonuclease-1 During DNA Replication And Cell Cycle Progress

During nuclear DNA replication, proofreading-deficient DNA polymerase a (Pol a) initiates Okazaki fragment synthesis, but does so with much lower fidelity than bulk replication by proofreading-proficient Pol δ or Pol ε. Pol a errors are corrected by MSH2-dependent mismatch repair. Here we provide evidence that mammalian FEN1 contributes to this repair. We show that MSH2 interacts with FEN1 and facilitates its nuclease activities to remove mismatches near the 5’ends of DNA substrates, in a process referred to as a-segment error editing (AEE). Mutations in FEN1 that reduce its endonuclease and exonuclease activities lead to AEE deficiencies in vitro, and mice harboring these mutations exhibit a strong mutator phenotype, enhanced cellular transformation and increased cancer susceptibility. The results identify a novel FEN1/MutSa interaction as a driving force in AEE and carcinogenesis.FEN1 as a nuclease, if the functions and locations can’t be executed precisely, genetic information coded in DNA may be attacked, which cause disorder to the programmed cell cycle. For that reason, the fate of the FEN1 once it dissociates from the PCNA and DNA at the exit of S phase is a question. Previous data showed that FEN1 express level is varied during cell cycle, and it is degradated in G2/M phase through ubiqutin-proteasome degradation pathway. In this project, I set up a Co-Immunoprecipation technology followed MS detect system and discovered all the three ubiquitination enzymes specific for FEN1: activated El (UBE1), conjungated E2 (UBE2M), and ligase E3 (PRP19).Based on the model of sequential modifications to degrade FEN1, methylated FEN1 would be demethylated before dissociate with PCNA. In the study, we validated that demethylation of FEN 1 occurs during S phase and UV treatment. In order to determine the specific arginine demethylase for FEN1, we employed co-immunoprecipitation technology and MS system and caught a Jmjc family demethylase JMJD1B. After a serial of biochemical detection, we can make a conclusion that JMJDIB can specifically demethylate FEN1, which indicated that we identified a novel nonhistione arginine demethylase.