Dependence of Ypt1 and Sec4 membrane attachment on Bet2

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Abstract
MANY small GTP-binding proteins are synthesized as soluble proteins that are post-translationally modified as a prerequisite for membrane attachment1. Ypt1 and Sec4 are homologous Ras-like 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 membranes2–6. Here we show that BET2, initially identified as a gene required for transport from endoplasmic reticulum to Golgi apparatus in yeast7, 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 prenyl-transferase that modifies Ras8, enabling it to attach to membranes9,10. We propose that Bet2 modifies Ypt1 and Sec4 in an analogous manner.