After being activated by an insertion/deletion loop (IDL), MSH2:MSH3 (MutSbeta) recruits MLH1:PMS2 (MutLalpha) (Iyer et al. 2010, Pluciennik et al. 2013) and interacts with PCNA (Iyer et al. 2010). As inferred from yeast, more than one molecule of MLH1:PMS2 may bind per molecule of MSH2:MSH3 (Hombauer et al. 2011). MLH1:PMS2 and PCNA compete for the same binding site on MSH2:MSH3 (Iyer et al. 2010). The interaction with PCNA determines which strand of DNA will serve as template and which strand will be repaired (Zhang et al. 2005, and inferred from MSH2:MSH6).