Extended Data Fig. 10: Model variants.
From: PCNA activates the MutLγ endonuclease to promote meiotic crossing over
Comparison of variations on the basic theme that MutLγ mediates crossover-specific dHJ resolution by catalysing strand-specific incisions on both sides of the two HJs. a, The model presented in Fig. 4h is shown for comparison. This version has recombination-associated DNA synthesis tracts terminating outside the dHJ. PCNA at these termini direct the MutLγ–MutSγ–Exo1 ensemble to incise upstream (5′) specifically on the strands with DNA synthesis, maintaining this specificity across the stacked junctions (lower panels). Resolution of HJ-1 results in a crossover whereas HJ-2 is resolved as a non-crossover. Notably, this version of the model produces only ‘pattern 1’ crossovers, shown previously to be promoted by MutLγ3. b, By contrast, a more canonical scheme, with synthesis tracts and associated PCNA molecules located within the dHJ produces ‘pattern 2’ crossovers, thereby disfavouring this version of the model. c, Pattern 1 crossovers are also produced by a variant of the model in which MutLγ–MutSγ–Exo1 incises downstream (3′) of the internal synthesis tracts. However, this polarity is opposite to that established for MMR12,13.
