FIGURE 6:

Positive charges in the Spo21 N terminus promote tetrad formation. (A) Distribution of ascal types in WT (AN120) ady4∆ (AC18), spo21-3A (GND4), and GND4 transformed with plasmids expressing SPO21 (pRS426-Spo21), ADY4 (pRS426-Ady4-GST), MSS4 (pRS424-Mss4), or STT4 (pRS426-Stt4). Each strain was sporulated and the number of spores per ascus was scored by light microscopy. For each strain, 400 asci were scored in each of three independent experiments. (B) A schematic of nonsister dyad formation in cells heterozygous for the centromere-linked, spore autonomous, fluorescent marker P_YKL050c::TagBFP::TRP1. For cells packaging dyads randomly, 2/3 of the dyads formed will be nonsister dyads. (C) Representative images of asci of ady4∆ (AC18-cen), spo21::GFP (AN230-cen), and spo21-3A (GND9) from the experiments in panel A. Arrows highlight examples of nonsister dyads; arrowheads indicate sister dyads. Scale bars = 5 µm. (D) Quantification of dyad types in the strains in C. Four asterisks indicate the frequency of nonsister dyads in spo21-3A is significantly different than in spo21::GFP (p < 0.0001; Fisher’s exact test). Two asterisks indicate that the frequency of nonsister dyads in spo21-3A is significantly different from ady4∆ (p < 0.003). For spo21::GFP, n = 257 dyads scored one experiment; ady4∆ n = 325 dyads scored one experiment; spo21-3A, at least 90 dyads scored in each of three independent experiments.