Mechanism of 5'-directed excision in human mismatch repair.
We have developed a purified system that supports mismatch-dependent 5'-->3' excision. In the presence of RPA, ATP, and a mismatch, MutSalpha activates 5'-->3' excision by EXOI, and excision terminates after removal of the mispair. MutSalpha confers high processivity on EXOI, and termination is due to RPA-dependent displacement of this processive complex from the helix and a weak ability of EXOI to reload at the RPA-bound gap in the product, as well as MutSalpha- and MutLalpha-dependent suppression of EXOI activity in the absence of a mismatch cofactor. As observed in the purified system, excision directed by a 5' strand break in HeLa nuclear extract can proceed in the absence of MutLalpha or PCNA, although 3' excision in the extract system requires both proteins.
Genschel
Jochen
J
Department of Biochemistry, Box 3711, Duke University Medical Center, Durham, NC 27710, USA.
Modrich
Paul
P
D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D001426:Bacterial Proteins; D020137:Base Pair Mismatch; D002467:Cell Nucleus / Q000737:chemistry; D004247:DNA / Q000235:genetics / Q000378:metabolism*; D004260:DNA Repair; D045643:DNA Repair Enzymes; D004268:DNA-Binding Proteins / Q000378:metabolism; D004789:Enzyme Activation; D029968:Escherichia coli Proteins / Q000378:metabolism; D005090:Exodeoxyribonucleases / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D000070956:MutL Proteins; D051719:MutS DNA Mismatch-Binding Protein; D051716:Replication Protein A
D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; C074770:MutL protein, E coli; C497167:RPA1 protein, human; D051716:Replication Protein A; D000255:Adenosine Triphosphate; D004247:DNA; C114331:EXO1 protein, human; D005090:Exodeoxyribonucleases; C028450:exodeoxyribonuclease I; D000251:Adenosine Triphosphatases; D000070956:MutL Proteins; D051719:MutS DNA Mismatch-Binding Protein; C497175:MutS protein, E coli; D045643:DNA Repair Enzymes