HARP preferentially co-purifies with RPA bound to DNA-PK and blocks RPA phosphorylation

Abstract

The HepA-related protein (HARP /SMARCAL1) is an ATP -dependent annealing helicase that is capable of rewinding DNA structures that are stably unwound due to binding of the single-stranded DNA (ssDNA)-binding protein Replication Protein A (RP A). HARP has been implicated in maintaining genome integrity through its role in DNA replication and repair, two processes that generate RP A-coated ssDNA. In addition, mutations in HARP cause a rare disease known as Schimke immuno-osseous dysplasia. In this study, we purified HARP containing complexes with the goal of identifying the predominant factors that stably associate with HARP. We found that HARP preferentially interacts with RP A molecules that are bound to the DNA-dependent protein kinase (DNA-PK). We also found that RP A is phosphorylated by DNA-PK in vitro, while the RP A-HARP complexes are not. Our results suggest that, in addition to its annealing helicase activity, which eliminates the natural binding substrate for RP A, HARP blocks the phosphorylation of RP A by DNA-PK. © 2014 Landes Bioscience.