REINVESTIGATION OF THE FUNCTIONS OF THE HYDROPHOBIC SEGMENT OF JEM1P,A YEAST ENDOPLASMIC-RETICULUM MEMBRANE-PROTEIN MEDIATING NUCLEAR-FUSION

Jem1p is a DnaJ-like protein of the yeast ER membrane, which is requir ed for nuclear membrane fusion during mating. We have determined the p osition of translation initiation codon for the JEM1 gene. Translation of Jem1p starts from the second ATG codon of the previously assumed J EM1 open reading frame, leading to the synthesis of a precursor protei n of 645 amino acids long. The translated Jem1p precursor contains an N-terminal hydrophobic sequence that functions as a signal sequence an d is removed upon import into the ER lumen. Jem1p is peripherally asso ciated with the ER membrane probably through protein-protein interacti ons. (C) 1998 Academic Press.