The core protein of alphaviruses. 2. Purification of peptides and complete amino-acid sequence of Sindbis virus core protein.

The primary structure of the core protein of Sindbis virus has been established by protein chemical characterization of peptides derived by enzymatic digestion with trypsin, pepsin and thermolysin and by chemical cleavage with cyanogen bromide. The peptide chain consists of 264 amino acids and has the composition Asp8, Asn8, Thr17, Ser12, Glu12, Gln14, Pro28, Gly24, Ala22, Val16, Met10, Ile8, Leu14, Tyr4, Phe9, His6, Lys25, Arg23 and Trp4 and an Mr of 29 382. Comparison of this structure with the primary structure of the SF virus core protein revealed several important common characteristics of alphavirus core proteins. 1. The N-terminal halves (1-110) of the proteins are rich in basic amino acids and proline. 2. The C-terminal part (approximately equal to 110-264/267) is highly conserved: 70% of the amino acid residues are in identical positions. 3. The conserved part contains a possible catalytic centre for the presumed protease activity of the core protein. The similarities between the primary structures of both core proteins are reflected in their predicted secondary structures.