Guo Shuangli, Zhang Yanbin, Yuan Fenghua, Gao Yin, Gu Liya, Wong Isaac, Li Guo-Min
Department of Molecular & Cellular Biochemistry and Markey Cancer Center, University of Kentucky Medical Center, Lexington, Kentucky 40536.
Graduate Center for Toxicology and Department of Pathology, University of Kentucky Medical Center, Lexington, Kentucky 40536.
J Biol Chem. 2006 Aug 4;281(31):21607-21616. doi: 10.1074/jbc.M603504200. Epub 2006 May 26.
Replication protein A (RPA) is involved in multiple stages of DNA mismatch repair (MMR); however, the modulation of its functions between different stages is unknown. We show here that phosphorylation likely modulates RPA functions during MMR. Unphosphorylated RPA initially binds to nicked heteroduplex DNA to facilitate assembly of the MMR initiation complex. The unphosphorylated protein preferentially stimulates mismatch-provoked excision, possibly by cooperatively binding to the resultant single-stranded DNA gap. The DNA-bound RPA begins to be phosphorylated after extensive excision, resulting in severalfold reduction in the DNA binding affinity of RPA. Thus, during the phase of repair DNA synthesis, the phosphorylated RPA readily disassociates from DNA, making the DNA template available for DNA polymerase delta-catalyzed resynthesis. These observations support a model of how phosphorylation alters the DNA binding affinity of RPA to fulfill its differential requirement at the various stages of MMR.
复制蛋白A（RPA）参与DNA错配修复（MMR）的多个阶段；然而，其在不同阶段功能的调节尚不清楚。我们在此表明，磷酸化可能在MMR过程中调节RPA的功能。未磷酸化的RPA最初与带切口的异源双链DNA结合，以促进MMR起始复合物的组装。未磷酸化的蛋白优先刺激错配引发的切除，可能是通过协同结合产生的单链DNA缺口。在广泛切除后，与DNA结合的RPA开始被磷酸化，导致RPA的DNA结合亲和力降低数倍。因此，在修复性DNA合成阶段，磷酸化的RPA很容易从DNA上解离，使DNA模板可用于DNA聚合酶δ催化的再合成。这些观察结果支持了一个关于磷酸化如何改变RPA的DNA结合亲和力以满足其在MMR各个阶段的不同需求的模型。
