FIG. 1.

Schematic of the Sindbis virus capsid protein and sequences of helix I mutants. (A) The SINV CP is shown schematically. Residues 1 to 76 are predominantly positively charged, except for residues 38 to 55 which are uncharged and form helix I. Residues 76 to 132 (hatched box) are implicated in specific binding of the genomic RNA. This region is also important for CP-CP interactions during core assembly. Residues 114 to 264 form the protease domain responsible for autocatalytic cleavage of the CP from the structural polyprotein. This domain is also involved in CP-CP and CP-glycoprotein interactions. (B) Sequences for chimeric viruses and mutants within helix I and their corresponding plaque phenotypes determined 48 h postinfection on BHK cells. The amino acids in bold type are the amino acids of the foreign sequence inserted instead of amino acids 35 to 57 of the SINV CP (helix I). The numbers in parentheses in the virus designations indicate the amino acids of the foreign sequence that was inserted or substituted. Identical amino acids at a given position are indicated by dashes. SINV/GCN4(255-277)(L268D) is identical in sequence to SINV/GCN4(255-277) except for the change at residue 268. Plaque phenotypes are as follows: VSP, very small plaque (<2.0 mm in diameter); SP, small plaque (2.0 to 2.5 mm); MP, medium plaque (2.5 to 3.5 mm); LP, large plaque (3.5 to 4 mm); NR, not recovered.