The signal sequence of the p62 protein of Semliki Forest virus is involved in initiation but not in completing chain translocation

Eventually, the signal sequence of the p62 protein becomes translocated across the membrane of the ER into its lumenal space. In here it is found as a glycosylated peptide which is part of a 66 amino acid residues long "pro-piece of the p62 protein. This pro-peptide, called E3, is cleaved at a late stage during virus assembly (de Curtis and Simons, 1988) and is then either released into the extracellular medium as a soluble protein (Sinbis virus) or remains as a peripheral protein subunit on the virus spike (SFV) (Garoff et al., 1982; Mayne et al., 1984) . Our present tests of the p62-globin and p62 dhfr hybrids in the high pH wash assay of membrane supplemented in vitro mixtures also support the notion that the p62 signal sequence does not remain bound to the membrane where it has exerted its function as a translocation signal.