Component of the 9-1-1 cell-cycle checkpoint response complex that plays a major role in DNA repair.The 9-1-1 complex is recruited to DNA lesion upon damage by the RAD17-replication factor C(RFC)clamp loader complex.Acts then as a sliding clamp platform on DNA for several proteins involved in long-patch base excision repair(LP-BER).The 9-1-1 complex stimulates DNA polymerase beta(POLB)activity by increasing its affinity for the 3'-OH end of the primer-template and stabilizes POLB to those sites where LP-BER proceeds;endonuclease FEN1 cleavage activity on substrates with double,nick,or gap flaps of distinct sequences and lengths;and DNA ligase I(LIG1)on long-patch base excision repair substrates.The 9-1-1 complex is necessary for the recruitment of C12orf32/RHINO to sites of double-stranded breaks(DSB)occurring during the S phase.RAD9A possesses 3'->5' double stranded DNA exonuclease activity.Its phosphorylation by PRKCD may be required for the formation of the 9-1-1 complex.