Gene conversion and intragenic recombination at the SUP6 locus and the surrounding region in Saccharomyces cerevisiae.

Spontaneous secondary mutations of the ochre suppressor SUP6 were selected in a haploid strain of Saccharomyces cerevisiae. Unselected tetrads were dissected from crosses heterozygous for one of three allleles of SUP6 and for three other loci in this region which span a length of 14 map units (his2, cdc14 and met10). The study showed that all of these markers were characterized by high frequency of meiotic gene conversion and long conversion lengths which frequently extended into adjacent marked loci. Despite the high conversion frequency of SUP6, recombination between alleles of this locus reached a maximum frequency of only 2 x 10(-3) protrophs/spore. Although the allelic recombination frequencies were not distance dependent and consequently could not be used to order the alleles, the inequality between the two recombinant outside marker combinations among selected intragenic recombinants produced an internally consistent map of the suppressor locus. Recombination at SUP6 (whether detected as conversion in tetrads or the production of recombinants among random spores) was accompanied by significantly less than 50% outside marker recombination.