The nucleotide sequence of intracellular 26S mRNA of Sindbis virus has been determined by direct sequence analysis of the cDNA made to this RNA with reverse transcriptase. From this, the amino acid sequences of the encoded virus structural proteins, which include a basic capsid protein and two integral membrane glycoproteins, have been deduced. The features of these proteins as related to their functions are discussed. We suggest that three proteases are required to produce these proteins from their polyprotein precursor: a viral protease, which functions in the cytosol to release the capsid protein, signalase, which makes two cleavages to separate the glycoproteins; and a protease of the Golgi complex that cleaves after double basic residues, to process the precursor form of one of the glycoproteins.
