Chemistry of crossing-over

Influence of edeine on intergenic and interallelic recombination in Neurospora crassa

The effect of edeine and the mutation edr-2 to edeine resistance on genetic recombination in Neurospora crassa was investigated. For this purpose crosses between pairs of edeine sensitive and edeine resistant strains respectively were set up without or in the presence of the drug (0-750 microg/ml). The genetic markers ylo-1, ad-1, pan-2 (B3 and B5) and tryp-2, all on linkage group VI, were used for scoring recombinants. These were ad+, tryp+ (intergenic recombination) and pan+ (interallelic recombination). Frequencies of about 6-7% for intergenic and of about 0.4% for interallelic recombination were found in crosses between eds strains and ed(r) strains respectively, if edeine was absent. However, crosses in the presence of edeine gave higher frequencies of both intergenic and interallelic recombination (about 12% intergenic and 1% interallelic with 180 to 200 microg ed/ml). The pan+ prototrophs (interallelic recombinants) obtained in the different crosses were tested for distribution of outside markers. The data thus obtained revealed that under the effect of both the mutation to edeine resistance and edeine itself the relative number of noncrossover (gene conversion) recombinants decreases in favour of crossover recombinants, and the relative number of double crossover recombinants (events outside the pan locus) decreases in favour of single crossover recombinants. It is concluded that a) edeine and the mutation ed(r)-2 to edeine resistance affect recombination via related pathways, and b) noncrossover and crossover recombinants are caused by different molecular mechanisms, in agreement with the work of other authors.