Fig. 7. RPA-TN and MLH1 dynamics. (A) A full-length pachytene SC with eight RPA-TN foci (TN, carets) and one recombination nodule (RN, elliptical bullet). (B) High resolution of the bracketed segment in A. The 10-nm gold grains mark the positions of RPA protein and the 5-nm particles that of the MLH1 protein. Colocation of 10-nm and 5-nm gold grains at the RN suggests that the RN is derived from a TN. Other TNs have relocated from their positions between the lateral elements of the SC to the periphery of the lateral elements. (C) Same as B but the twist in the SC shows that the RN is on the surface of the SC. (D) Okadaic acid treatment of spermatocytes causes premature separation of the lateral elements (FITC, green). The TNs are no longer between the cores but are associated with the cores. Inset: RNs (green foci), by contrast, remain between the separated lateral elements (red) at the positions of the chiasmata. (E) Summary of RPA-TN and MLH1-RN dynamics for 12 mouse spermatocyte nuclei. MLH1 foci appear when the number of TNs has been reduced to about 100 foci per nucleus. Image in A and data for Table 2 were derived from SCs in the bracketed portion of the graph.