FIG. 1.

Primary structure of VP4 and location of amino acid changes. The cDNA of RRV VP4 encodes a protein containing a predicted 776 amino acids (88 kDa). Proteolytic cleavage of the precursor VP4 to two noncovalently associated subunits, VP8* (28 kDa) and VP5* (60 kDa), is required for infectivity. Cleavage has been shown to occur after three different arginine residues (arginine 231, arginine 241, and arginine 247) within a predicted exposed loop, the TCR (1). These residues were changed to histidine residues by site-directed mutagenesis (25) either individually (to create R231H, R241H, and R247H, respectively) or as a group (to create NC). The mutations were confirmed by sequencing on an ABI automated DNA sequencer. The putative fusion peptide sequence from sites 385 to 410 is shown.