Figure 5.

Proposed mechanisms of MutSβ-mediated trinucleotide repeat instability. Impaired MutSβ ATP-binding and sliding clamp formation would prevent loop cleavage by MutLα resulting in expansion. Alternatively, improper PCNA loading may result in dysregulated strand discrimination by MutLα and cleavage on either strand (indicated by a red arrow). This would result in tract expansion, contraction or DSB formation. (see colour version of this figure at www.tandfonline.com/ibmg)