1D)

1D). onto ssDNA overhangs. Metnase-induced enhancement of Exo1-mediated DNA strand resection required the presence of these overhangs but did not require Metnase’s DNA cleavage activity. These results suggest that Metnase enhances Exo1-mediated exonuclease activity around the lagging strand DNA by facilitating Exo1 loading onto a single strand gap at the stalled replication fork. Keywords: DNA-binding protein, DNA damage, DNA enzyme, DNA repair, DNA replication == Intro == DNA-damaging agents as well as inhibitors of deoxyribonucleotide synthesis and DNA polymerase action block the progression of replication forks (1, 2). Replication fork stalling induces uncoupling between DNA polymerases and the replicative DNA helicases and produces stretches of ssDNA2on both strands that Aumitin are exposed to nuclease attack (17). Replication fork repair and restart in eukaryotes are complex and poorly comprehended (1, 5, 7, 8). Upon replication fork arrest from deoxyribonucleotide depletion after hydroxyurea (HU) treatment, uncoupling of DNA polymerases and helicase produces ssDNA overhangs on both leading and lagging strands. Restart of stalled replication forks can occur via the reannealing of ssDNA, or forks can undergo regression and pairing from the newly synthesized strands to form a Holliday junction structure (chicken foot). When free 5-ends are present, end resection creates 3-ssDNA on which Rad51 can load, and Rad51-mediated DNA displacement loop formation eventually allows reloading of the replication machinery intended for fork restart. Rad51-mediated homologous recombination (HR) also mediates fork reversal for restart of replication (9, 10). Holliday junctions can also be processed into a one-ended double strand break (DSB), and fork restart is then achieved through Rad51-mediated homologous recombination repair (1, 5, 7, 8). Although homologous recombination repair is a preferred pathway in restart of stalled replication forks (1, 5, 8, 11, 12), the comprehensive mechanism(s) and the factors involved are not well understood. Stalled replication forks often require the generation of an intrinsic DSB to begin the 5-end Rabbit Polyclonal to Catenin-gamma resection that initiates recombination-mediated fork repair (1, 7, 8, 13, 14). The Aumitin stressed fork can do this Aumitin in at least two ways: the fork can reverse into a chicken foot structure with a one-sided DSB, or a nuclease can Aumitin generate a DSB at the stalled fork as part of the restart process. If a Aumitin stalled fork is not repaired, it can collapse into a variety of structures that make restart hard (8, 1517) and can result in genomic instability, leading to cell death or neoplastic change (2, 8, 11). Repair pathway choice at stalled forks is important for genomic stability because unopposed classical non-homologous end joining (cNHEJ), such as seen in malignancies with inherited BRCA1 or BRCA2 deficiencies, leads to fusion from the one-sided DNA ends at damaged replication forks (12, 1822). These chromosomal fusions at stalled forks can cause severe genome instability, resulting in catastrophic mitoses with gross nuclear abnormalities, such as nuclear bridges and micronuclei (8, 12, 18, 21, 23). Preventing cNHEJ by repressing 53BP1 rescues these nuclear defects (19). Thus, HR is the preferred repair pathway for stalled replication forks to prevent genomic instability (1, 5, 8, 11, 12). There is accumulating evidence that DSB pathway choice between cNHEJ and HR is mediated by 5-end resection (13, 14, 24). End resection intended for HR is likely a two-step process where CtIP and Mre11 nucleolytically resect brief 5-tracks with Dna2 and particularly Exo1 resecting longer trails (13, 12, 17, twenty-five, 26), making long 3-ss-tracts. The choice among different DSB repair path ways is snugly regulated, and DNA end resection presents a primary regulating step (27). The ssDNA tails designed at DSBs also enjoy.