DEPENDENCE OF YPT1 AND SEC4 MEMBRANE ATTACHMENT ON BET2

MANY small GTP-binding proteins are synthesized as soluble proteins that are post-translationally modified as a prerequisite for membrane attachment 1. Ypt1 and Sec4 are homologous Raslike GTP-binding proteins that have been proposed to regulate the specificity of vesicular traffic at different stages of the secretory pathway by cycling on and off membranes 2-6. Here we show that BET2, initially identified as a gene required for transport from endoplasmic reticulum to Golgi apparatus in yeast 7, encodes a factor that is needed for the membrane attachment of Ypt1 and Sec4. DNA sequence analysis has revealed that Bet2 is homologous to Dpr1 (Ram1), an essential component of a protein prenyltransferase that modifies Ras 8, enabling it to attach to membranes 9,10. We propose that Bet2 modifies Ypt1 and Sec4 in an analogous manner.