Marker-specific effects in genetic recombination

Abstract

The recombination frequencies between mutants in the lac operon of Escherichia coli are primarily determined by the base substitution at a mutant site and the neighboring nucleotide sequence. Distance appears to be of no importance in the recombination between these mutants although there is a suggestion that when markers are separated by less than tens of nucleotides distance does become important. The substitution of one nucleotide pair for another at a mutant site may result in order of magnitude changes in recombination frequency. In addition the recombination frequency between a pair of mutants may be affected by the presence of an additional misspaired nucleotide, at some distance from either mutant site. Marker-specific effects are found with both missense and nonsense mutants and do not appear to be related to the polarity of nonsense mutants. In this regard, the presence of a new site for the initiation of translation, which relieves the polarity of proximal nonsense mutants, has no effect on the recombination properties of these mutants. Marker-specific effects are not observed when the lac mutants are crossed with the uracil locus, approximately 10 6 nucleotide pairs away. High negative interference was observed in these studies. Those markers which tended to be strong recombiners in two-factor crosses also tended to yield a large excess of multiple recombinants in three-factor crosses, irrespective of distance.