Final answer:
In the yeast mismatch repair system, proteins Msh2, Msh3, and Msh6 work together to recognize and repair mismatches, where Msh2 pairs with Msh3 or Msh6 to identify DNA errors.
Step-by-step explanation:
In yeast, the mismatch repair system is a vital mechanism for correcting errors that occur during DNA replication. Proteins known as Msh2, Msh3, and Msh6 work collaboratively to recognize and repair mismatches.
Specifically, Msh2 pairs with either Msh3 or Msh6 to form heterodimers that scan the DNA for mismatches. The answer to the question is A. Msh2; Msh3 and Msh6, with Msh2 acting in concert with Msh3 or Msh6 to recognize mismatches, while the combinations of Msh3/Msh6 act as specificity factors to target various types of base mispairings.