Characterization of a cDNA encoding a subunit of the rat brain rsec6/8 complex

Many proteins required for neurotransmission are homologous to proteins involved in the Golgi-to-plasma membrane stage of the yeast secretory pathway. A novel 17S complex composed of eight proteins including rsec6 and rsec8, the rat homologues of the yeast secretory proteins, Sec6p and Sec8p, has been identified in rat brain cytosol. Sec6p and Sec8p are components of a complex of at least seven proteins which are essential for secretion in yeast. While the complementary DNAs (cDNA) encoding rsec6 and rsec8 have been cloned, the other six components of the 17S complex remain undescribed. Using the peptide sequence obtained from p71, one of the subunits of the rat brain 17S complex, we isolated a full-length cDNA from a rat brain library. This cDNA is predicted to encode a hydrophilic protein of 82 kDa, similar in size to that observed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) for the endogenous rat brain rsec6/8 complex 71 kDa component. p71 contains domains of peptide sequence which display significant homology to regions of the tail domain of yeast type II myosin. Northern blot analysis of rat tissues indicates that messenger RNA transcripts of 3.1 and 4.4 kb encoding this protein are expressed broadly across several rat tissues in a pattern similar to that of rsec6 and rsec8 mRNA expression. A possible role for p71 as a point of interaction for proteins of the cytoskeleton and proteins involved in secretion is discussed.