A crossover hotspot near his-3 in Neurospora crassa is a preferential recombination termination site

During analysis of 148 unselected Neurospora crassa octads, an above average rate of crossing over was detected within a 360-base region near the 3′ end of his-3, suggesting a hotspot for crossing over about 1.8 kb away from the recombination initiation site within cog. Homozygous deletion of the 360-base region increases exchanges in his-3 and on the far side of his-3 from cog, with the heterozygote showing an intermediate increase. We conclude that recombination events initiated at cog terminate within the 360-base sequence more often than in other sections of the cog-his-3 interval and, since some of these terminations will be resolved as crossovers, a cluster of crossovers at this location is the outcome. Removal of this termination site increases the chance that an event will reach his-3, resulting in recombination within the gene, or extend past it to yield a crossover on the other side of his-3. The deleted sequence has substantial predicted secondary structure, including a complex predicted stem-loop, suggesting that DNA secondary structure may be responsible for the termination.