Complementation between Ad-5/7 Alleles in Yeast.

NTRAGENIC complementation occurs when a full or partial restoration of 'nonmutant phenotype results from the association of two different mutant alleles in a heterozygote, heterocaryon, or heterogenote. It has been demonstrated for a number of gene loci in a variety of microorganisms which include fungi. (FINCHAM and PATEMAN 1957; GILES, PARTRIDGE and NELSON 1957; CATCHESIDE and OVERTON 1958), bacteria (HARTMAN, HARTMAN, SERMAN and LOPER 1958; MORSE 1962), and bacteriophage (CHAMPE and BENZER 1962). It has also been shown to occur in Drosophila (CARLSON 1959; WELSHONS and VON HALLE 1960; GREEN 1961; DORN and BURDICK 1962). In 1958 CATCHESIDE and OVERTON showed that the pattern of relationships between complementing alleles could be recorded as a simple two-dimensional matrix and could be represented topographically as a simple straight line with distinct end points, which they called a complementation map. The relationship of alleles of most of the gene loci already studied can be represented in this manner. Recently. however, an increasing number of complementation maps have been reported which cannot be portrayed in this manner. Some of these are linear but do not possess end points (CARLSON 1961; CHAMPE and BENZER 1962; GROSS 1962; KAPULER and BERNSTEIN 1962), others are nonlinear ( CATCHESIDE 1960; ISHIKAWA 1960, 1962a, 196213; BERNSTEIN and MILLER 1961; BEVAN and WOODS 1962; SUYAMA and BONNER 1962; WOODWARD 1962). In this report, a further exception is described. Data are presented which show that the complementing ad-7 mutant alleles of Saccharomyces cerevisiae may be mapped as a circle with a short tail segment. ROMAN (1956a) was the first to isolate what he termed ad-5 and ad-7 mutant strains. These, when crossed, produced prototrophic diploids and he concluded that they were mutants of two different gene loci. He further concluded that these loci were closely linked since they were inseparable in 163 meiotic segregations. At the same time. ROMAN reported that mutation frequently affected both the ad-5 and ad-7 loci simultaneously to give what he termed ad-5 ad-7 strains. (The symbol ad is used throughout the text to represent alleles conferring a growth requirement for adenine.) This finding has been confirmed both by DORFMAN 11963, 1964) and by the results of the present work. CATCHESIDE ( 1958) later interpreted this situation as a case of intragenic complementation, and MORTIMER (1963) states that he considers ad-5 and ad-7 alleles to be mutations of a single locus.