Analysis of Semliki-Forest-virus structural proteins to illustrate polyprotein processing of alpha viruses.

The four structural proteins of Semliki Forest virus were purified in an amount of 30-50 nmol by preparative sodium dodecylsulfate/polyacrylamide gel electrophoresis. Each protein was subjected to N-terminal structural analysis by degradation in a liquid-phase sequencer. About 20 residues were determined for each of the two membrane glycoproteins E1 and E2. The amino acid sequence of E1 but not that of E2 showed extensive homology to the corresponding proteins of the closely related Sindbis virus. Both E1 and E2 seem to lack a signal sequence at the N terminus, since the proportion of polar amino acids in this region deviates from the proportion in the known hydrophobic signal sequences. The envelope glycoprotein E3 and the capsid protein did not yield any significant result on Edman degradation, suggesting that they have blocked N-terminal amino groups.