NEW MUTANTS OF SACCHAROMYCES-CEREVISIAE AFFECTED IN THE TRANSPORT OF PROTEINS FROM THE ENDOPLASMIC-RETICULUM TO THE GOLGI-COMPLEX

We have isolated new temperature-sensitive mutations in five complemen tation groups, sec31-sec35, that are defective in the transport of pro teins fr-om the endoplasmic reticulum (ER) to the Golgi complex. The s ec31-sec35 mutants and additional alleles of previously identified sec and vacuolar protein sorting (vps) genes were isolated in a screen ba sed on the detection of ct-factor precursor in yeast colonies replicat ed to and lysed on nitrocellulose filters. Secretory protein precursor s accumulated in sec31-sec35 mutants at the nonpermissive temperature were core-glycosylated but lacked outer chain carbohydrate, indicating that transport was blocked after translocation into the ER but before arrival in the Golgi complex. Electron microscopy revealed that the n ewly identified sec mutants accumulated vesicles and membrane structur es reminiscent of secretory pathway organelles. Complementation analys is revealed that sec32-1 is an allele of BOS1, a gene implicated in ve sicle targeting to the Golgi complex, and sec33-1 is an allele of RET1 , a gene that encodes the alpha subunit of coatomer.