Abstract
Genetic and nutritional analyses have been made of 7 purineless and 2 pyrimidineless mutants of S. cerevisiae. Allelism tests revealed 5 different genetic types in the purine- requiring group, 2 in the pyrimidine- requiring group. The purine auxotrophs could grow only on adenine or hypoxanthine and were competitively inhibited by guanine. Uracil, cytosine, 5-nitrouracil, uridine, and uridylic acid could be used by both pyrimidineless mutants.