Isolation and characterization of Saccharomyces cerevisiae mutants deficient in S-adenosylmethionine decarboxylase, spermidine, and spermine

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Abstract
Four mutants were isolated from S. cerevisiae that are deficient in S-adenosylmethionine decarboxylase (spe2). All 4 mutants are chromosomal and fall into a single complementation group tightly linked to arg1. Since one of the mutants contained a temperature-sensitive activity, this complementation group defines the structural gene. Mutants totally lacking enzymic activity did not contain spermidine or spermine and had a greatly increased doubling time when grown in the absence of these 2 polyamines. Addition of 10-6 M spermidine or 10-5 M spermine, but not putrescine or cadaverine, restored the doubling time to that of the wild type. Diploids formed from a cross of 2 mutants completely deficient in spermidine and spermine were unable to sporulate in the absence of added spermidine or spermine. Evidence was obtained that arg1 was not located on any of the 17 known chromosomes; possibly arg1 and spe2 are located on a new 18th chromosome.