Answer to Question 3 from November, 2006

3a. (2 points) With which protein(s) does human MutSα-MutLα interact in order to distinguish the newly synthesized strand from the template strand at a mismatch?

RFC and PCNA. These two proteins bind to the 3'-OH ends generated in the newly synthesized strand during replication. Their selective binding to the newly synthesized strand permits MutSα-MutLα to distinguish the newly synthesized strand from the template strand.

3b. (3 points) List the final steps of mismatch repair in human cells, after MutSα-MutLα has identified the newly synthesized strand.

1. The PMS2 subunit of MutLα acts as an endonuclease to cleave the newly synthesized strand on the side of MutSα-MutLα opposite the RFC-PCNA complex.
2. Exonuclease I removes the newly synthesized strand, between the 3'-OH end bound by RFC-PCNA and the nick newly introduced by PMS2.
3. The resulting gap is filled in by DNA polymerase δ.
4. The resulting nick is sealed by DNA ligase I.

Return to Questions and Answers from previous exams.