Haemoprotein formation in yeast. II. Isolation of catalase regulatory mutants

A procedure was described for the isolation of mutants affected in the regulation of catalase activity. Two such mutants, cgr 1 and cgr 2 were obtained. Both of them show catalase activity that is resistant to repression by glucose, but is sensitive to anoxia to the same extent as the wild type.

Positive selection of general amino acid permease mutants in Saccharomyces cerevisiae

It was found that D-stereoisomers of natural amino acids inhibit the growth of Saccharomyces cerevisiae cells. Kinetic and genetic evidence showed that d-amino acids enter the cell by the general amino acid permease. Two classes of S. cerevisiae mutants resistant to d-amino acids were isolated. One class of mutants appeared to be defective in the general amino acid permease specified by the gene gap. In the second class, the activity of general amino acid permease was affected by ammonium ions. Mutants of the second class were isolated in a yeast strain with the general amino acid permease insensitive to the presence of ammonium ions in culture media. The mutation affecting the permease, amc, occurred in a locus unlinked to gap.

Nonsense mutations affecting the his4 enzyme complex of yeast

The his4 region of yeast contains the information necessary for the catalysis of three steps in the histidine biosynthetic pathway. The three activities specified by this region remain physically associated during gel filtration and ultracentrifugation and after extensive purification. Nonsense mutations in the "operator distal" his4C region lower the molecular weight of the two proximal activities. The proximal activities can, therefore, function without the his4C portion of the protein(s). These observations are compatible with the following three possibilities. The his4 region codes for: (1) an aggregate of three proteins forming a multiprotein complex; (2) a single protein with three catalytic activities; and (3) a single protein which is cleaved to form three proteins which remain associated.