GENE CONVERSION AND INTRAGENIC RECOMBINATION AT AT THE SUP6 LOCUS AND THE SURROUNDING REGION IN SACCHAROMYCES CEREVISIAE

Abstract

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 alleles 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 × 10-3 prototrophs/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.

Further observations on intragenic recombination inDrosophila melanogaster

“…The probability that a given gene conversion involves flanking marker exchange is markedly less than 50% in Drosophila melanogaster, an observation that is consistent with most of the fungal data (Stadler, 1973;DiCaprio & Hastings, 1976;Fogel et al 1978;Perkins, 1979). However, an apparent difference is that in Drosophila only one class of flanking marker exchange is recovered from each cross (See Table 2), in contrast to most fungal data which show both major and minor crossover classes.…”

DELETIONS OF THE ISO-1-CYTOCHROME c AND ADJACENT GENES OF YEAST: DISCOVERY OF THE OSM1 GENE CONTROLLING OSMOTIC SENSITIVITY

“…A SUP4-o strain containing the UAA alleles his5-2 and lysl-l was plated on hypertonic medium. Genetic analysis of one of the revertants, sup4-o-R, that had become auxotrophic for lysine and histidine, revealed that the loss of the suppressor activity was due to a second-site mutation in the SUP4 locus (see DICAPRIO and HASTINGS 1976;ROTHSTEIN 1977). To test whether certain deletions of the cycl gene extended into the closely-linked SUP4 locus, strains were constructed that contained the appropriate cycl deletion, as well as the markers lysl-1 and/or his5-2.…”