Figure 3.

Effect of nse6Δ mutation on the frequency of meiotic crossovers. (A) Crossover (CO) frequencies in three intervals in the wild-type and nse6Δ backgrounds. The percent of recombinant spore colonies was converted into genetic distance in centimorgans with Haldane’s equation. The number of colonies analyzed is the total from at least three independent experiments. (B) Amount of crossover DNA generated at the mbs1 hotspot (8). Diploid pat1-114 wild-type (GP6656), mus81Δ (GP6657), nse6Δ (GP6234) and nse6Δ mus81Δ (GP7765) strains with heterozygous restriction sites PmlI (L) and XbaI (R) flanking mbs1 were assayed. Digestion with these enzymes and PvuII (black arrowheads), which cuts outside L and R, gives two parental DNA fragments [9.2 kb (P1) or 6.8 kb (P2)] and two recombinant DNA fragments [11.2 kb (R1) or 4.8 kb (R2)] detected by the Southern blot hybridized probe (black lines at mbs1). The crossover DNA was measured at 7 h, after JM resolution in wild-type strains (Figure 4A, top); a pre-meiotic 0 h is shown as a control. Because R1 can also arise from incomplete digestion (R1^) at either L or R, the frequency of crossover DNA (% CO) was calculated as two times the amount of R2 DNA divided by the amount of total DNA. DNA from two independent inductions of strain GP7765 (nse6Δ mus81Δ) are shown. The means of two to three experiments (some from additional unpublished experiments) with the range or standard error of the mean are given. The asterisk indicates a non-specific cross-hybridization band.