Figure 4.

MutSβ binds to the individual strands of the FX repeat. Purified human MutSβ was added to reaction mixtures containing either a fully heteroduplex molecule (duplex) or otherwise duplex oligonucleotides containing the indicated repeat loop-outs at concentrations of 200 pM, 400 pM, 1 and 4 nm as described in the Materials and Methods. The DNA and DNA–MutSβ complexes were then analyzed as described in the Materials and Methods. Note that while some MutSβ binding to duplex DNA, a poor MMR substrate, can be seen (upper left panel), this binding is relatively inefficient as evidenced by the large fraction of unbound (free) probe.