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

Today there is no exact information about how a signal sequence might be inserted into the ER membrane when exerting its function in chain translocation. However, the typical cytoplasmic orientation of the NH2-termini of membrane protein chains carrying a combined signal sequence-anchoring peptide suggests that signal sequences in general might direct their function in translocation through the insertion of their hydrophobic and uncharged stretch of amino acid residues into the membrane in such an orientation that the NHEterminus of the signal remains on the outside of the ER mem- (Garoff et al., 1980; Rice and Strauss, 1981; Dalgarno et al., 1983; Kinney et al., 1986; Chang and Trent, 1987) . Amino acid residues are given using the one letter code and they are numbered from the NH2-towards the COOH-terminus. The boxes indicate that region in each sequence which best fulfills the consensus features of a signal sequence (the uncharged and hydrophobic region). The * symbols represent attachment sites for oligosaccharide and the (+) and (-) the presence of a charged amino acid side chain. Proline residues are labeled with a dot. The sequences are aligned according to maximum amino acid sequence homology.