FIG. 1.

(A) Schematic for the functional organization of nsP2 in the genus Alphavirus. The temperature-sensitive mutations (ts) that have been previously mapped to nsP2 helicase, protease, and the MTase-like domain are indicated. Mutations ts14, ts16, ts21, and ts19 are located in the helicase domain (62), and mutations ts18, ts17, ts133, and ts24 map to the protease domain (30). SFV ts4 is another mutation mapped to the extreme C terminus of nsP2 in SFV (71). (B) Location of the SINV nsP2 MTase-like domain residues chosen for mutagenesis on the VEEV nsP2pro structure. The N-terminal protease domain (residues 468 to 603) is shown in gray. The C-terminal MTase-like domain (605 to 787) is depicted in green. The mutated residues are labeled with VEEV numbering and SINV numbering in parentheses. The residues that were mutated in SINV are labeled with the VEEV numbering; e.g., SINV R615 is shown as VEEV R604 (Table 1). The residues are colored based on the plaque phenotype of the corresponding alanine mutants in SINV. Small plaque, blue; medium plaque, cyan. The ts lethal mutants are in magenta. The protease catalytic dyad and the residue that corresponds to the previously reported (23) noncytopathic mutation in SINV (SINV P726/VEEV P713), SIN/G, are indicated in orange.