| Research Abstract |
1. The role of Sar1p in vesicle formation from the endoplasmic reticulum (ER) was investigated in tenus of the regulation of its GTPase cycle. EKS1/HRD3 and SED4 were identified as multicopy suppressors of sar1 ts mutants and suggested to be good candidates of GTPase regulators.
2. The regulation of Sec12p, which is guanine-nucleotide exchange factor of Sar1p, was also studied genetically. A loss-of-function type mutation of HRR25, encoding a yeast casein kinase I, suppressed sec12 ts, suggesting that Hrr25p negatively regulates vesicle budding.
3. The functions of RERI and RER2, genes involved in correct ER localization of Sec 12p, were extensively studied. RERI was shown to encode a Golgi membrane protein, which was essential for retrieval of not only Sec12p but also Sec7lp and Sec63p from the Golgi to the ER. Their transmembrane domains contained Rer1p-dependent retrieval signal. On the other hand. RER2 was demonstrated to code for cis-prenyltransferase, a key enzyme of dolichol synthesis. In addition to the role in protein glycosylation, novel physiological roles of dolichol were suggested from the phenotypes of rer2.
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