The yeast plasma membrane uracil permease is stabilized against stress induced degradation by a point mutation in a cyclin-like "destruction box".

Yeast uracil permease appears to be fairly stable in exponentially growing cells, but it undergoes rapid endocytosis followed by degradation when cells are submitted to adverse conditions, such as nutrient starvation or inhibition of protein synthesis. Uracil permease has a sequence (RIALGSLTD) that is very similar to the "destruction box" of mitotic cyclins. This box is required for the ubiquitin-dependent proteolysis of cyclins. We replaced the invariant arginine residue of the putative "destruction box" in uracil permease by an alanine. The mutation significantly protected the permease against stress-induced degradation. This result suggests that ligation to ubiquitin could be a signal for uracil permease degradation.