The flk1 mutation, which was originally isolated in the yeast Saccharomyces carlsbergenesis, causes insensitivity to catabolite repression. This mutation has been further characterized and mapped. The gene flk1 is located on chromosome III between thr4 and MAL2, 14 centimorgans from MAL2. flk1 is shown to be allelic to the pleiotropic mutants tup1, cyc9, and umr7; and flk1 is shown to exhibit an array of pleiotropic properties common to tup1, cyc9 and umr7; These results suggest that the flk1 mutation is not a specific lesion affecting catabolite repression.