THE YEAST PLASMA-MEMBRANE URACIL PERMEASE IS STABILIZED AGAINST STRESS-INDUCED DEGRADATION BY A POINT MUTATION IN A CYCLIN-LIKE DESTRUCTIONBOX

Yeast uracil permease appears to be fairly stable in exponentially gro wing cells, but it; undergoes rapid endocytosis followed by degradatio n when cells are submitted to adverse conditions, such as nutrient sta rvation or inhibition of protein synthesis. Uracil permease has a sequ ence (RIALGSLTD) that is very similar to the ''destruction box'' of mi totic cyclins. This box is required for the ubiquitin-dependent proteo lysis of cyclins. We replaced the invariant arginine residue of the pu tative ''destruction box'' in uracil permease by an alanine. The mutat ion significantly protected the permease against stress-induced degrad ation. This result suggests that ligation to ubiquitin could be a sign al for uracil permease degradation. (C) 1994 Academic Press, Inc.