The effect of rec-2 on repeat-induced point-mutation (RIP) and recombination events that excise DNA sequence duplications at the his-3 locus in Neurospora crassa

In Neurospora crassa, duplicated DNA suffers both extensive repeat-induced point-mutation (RIP) and also excision by recombination events during the dikaryotic phase of the life cycle that precedes karyogamy and meiosis (reviewed by Selker 1990). This paper describes experiments designed to test the effect of rec-2, a gene known to modulate the local level of meiotic recombination at his-3, on RIP and the excision of tandem duplications. Duplications carrying his-3 sequences and a marker, hug ^r, that confers hygromycin resistance were constructed by targeted transformation. RIP and excisive recombination were assessed from the progeny of crosses heterozygous for a duplication and having different combinations of rec-2 alleles. In the presence of rec-2 ⁺, excision of hyg ^r was reduced to about half of that in crosses homozygous for rec-2. In contrast, rec-2 ⁺ had little influence on the frequency of duplications that escaped RIP. Thus, in addition to reducing recombination between his-3 alleles during meiosis, rec-2 ⁺ also influences recombination events that lead to the excision of duplications carrying his-3. However, RIP may be independent.