A restriction and modification model for the initiation and control of recombination inNeurospora

Abstract

SummaryIt is hypothesized that the products of Neurosporarec+genes mask recombinators such ascogby modifying DNA and that unmodified recombinators act as recognition sites for an endonuclease with scission properties like those of the type I restriction enzymes found inE. coli. These cut the DNA in both strands at some variable distance from a recognition site. Repair of a two strand gap initiated in this way would require DNA synthesis using the information contained in the homologous DNA duplex, leading to gene conversion. Crossing over could follow from resolution of two Holliday structures formed during gap repair. The hypothesis explains the polarity in the frequency of conversion events across genetic loci, the observation that chromosomes carrying recombinators are more often converted than is the homologue, and how recombinators can initiate conversion at a distance, as suggested by the pattern of conversion events in thehis-3locus in crosses heterozygous for the translocation TM429.