MAPPING CHROMOSOMAL GENES OF SACCHAROMYCES CEREVISIAE USING AN IMPROVED GENETIC MAPPING METHOD

Reed B. Wickner ¹

¹ Laboratory of Biochemical Pharmacology, National Institute of Arthritis, Metabolism, and Digestive Diseases, National Institutes of Health, Bethesda, Maryland 20205

A triploid (3n) strain of Saccharomyces cerevisiae was constructed carrying a standard marker on each of chromosomes I through XVII in the -/+/+ configuration. This is called a "supertriploid." Meiotic spores from this strain (n + n/2) were mated with a haploid (n) carrying an unmapped mutation. Meiotic analysis of each zygote clone (2n + n/2) produced in this way resulted in elimination of an average of 4.2 chromosomes as the possible location of the unmapped marker. The distribution of extra chromosomes in the 2n + n/2) strains was nearly random. Meiotic segregants of these crosses carrying the unmapped mutation in the -/+ configuration were then crossed with multiply marked haploid strains to further narrow the possible location of the unmapped mutation to a single chromosome. Scoring of markers by complementation tests was simplified by mating spore clones with mixtures of a and strains, each pair carrying the same set of markers. Using this new, more rapid method ("supertriploid mapping"), eight genes required for the maintenance of the killer plasmid were located on the genetic map of S. cerevisiae.