SCM2, a tryptophan permease in Saccharomyces cerevisiae, is important for cell growth

SCM2, a novel gene encoding a yeast tryptophan permease, was cloned as a high-copy-number suppressor of cse2-1. The cse2-1 mutation causes cold sensitivity, temperature sensitivity and chromosome missegregation. However, only the cold-sensitive phenotype of cse2-1 cells is suppressed by SCM2 at high copy. SCM2 is located on the left arm of yeast chromosome XV, adjacent to SUP3 and encodes a 65 kDa protein that is highly homologous to known amino acid permeases. Four out of five disrupted scm2 alleles (scm2 delta 1-delta 4) cause slow growth, whereas one disrupted allele (scm2 delta 5) is lethal. Cells with both the scm2 delta 1 and trp1-delta 101 mutations exhibit a synthetic cold-sensitive phenotype and grow much more slowly at the permissive temperature than cells with a single scm2 delta 1 or trp1-delta 101 mutation. A region of the predicted SCM2 protein is identical to the partial sequence recently reported for the yeast tryptophan permease TAP2, indicating that SCM2 and TAP2 probably encode the same protein.