| Abstract: | Three non-linked loci were found to be involved in thiamine excretion in Saccharomyces cerevisiae, i.e. thi2 which is complementary with thi3 and thi4, the latter two being substitutable mutually but acting also together. Mutation thi3 was present already in strain Nα, which produced relatively high frequencies of excreters after UV treatment. Non-excreting ‘revertants’ of unstable excreters derived from another haploid strain contained recessive mutation thi2, so that mutation thi3 can be substituted also by the metabolic or physiological disorders ruling after UV treatment. Mutations thi2 were found also in all 43 analysed stable excreting mutants obtained by UV treatment of strain Nα which indicates that they are either inevitable for the excretion or are specifically selected by the selection method used. At least one suppressor locus of thiamine excretion was present in that strain of S. cerevisiae, which did not produce thiamine excreters after UV treatment in spite of its ability to synthetise thiamine. |
