SED6 IS IDENTICAL TO ERG6, AND ENCODES A PUTATIVE METHYLTRANSFERASE REQUIRED FOR ERGOSTEROL SYNTHESIS

Luminal endoplasmic reticulum (ER) proteins carry a sorting signal tha t allows them to be retrieved from the Golgi apparatus by a specific r eceptor. In yeast, this receptor is encoded by the ERD2 gene. Although retrieval of ER proteins does not appear to be an essential process, cells lacking ERD2 do not grow. Several multicopy suppressors of this growth defect have been isolated. The sequence of one of these, SED6, is presented here. Its product contains motifs characteristic of methy ltransferases, and it is identical to ERG6, the presumed structural ge ne for ylmethionine:Delta(24)-sterol-C-methyltransferase. The gene is located adjacent to PDR4, near the centromere of chromosome XIII.