ABSTRACT
Saccharomyces cerevisiae secretes only a few proteins which are found in the medium, in the periplasmic space, or associated with the cell wall. The SEC 12 gene has been cloned; its DNA sequence predicts a protein of 471 amino acids containing a hydrophobic stretch of 19 amino acids near the C-terminal end. GTP-binding proteins are also involved as regulatory elements in the secretory pathway. A mammalian cell-free system has shed light on the role of NSF and GTP-binding proteins in transport through the Golgi apparatus by means of vesicles. An elaborate in vitro protein transport system used gently lysed spheroplasts that released cytosolic proteins but left organelles intact. Fluorescent antibodies directed against the YPT1 protein showed a punctate pattern in the cytoplasm. The SRP is then released from the complex, and translocation of the secretory protein takes place across the ER membrane.
