Maturation Defects in Temperature-sensitive Mutants of Sindbis Virus

Abstract

Temperature-sensitive mutants of Sindbis virus which synthesize viral RNA but not mature virus at the nonpermissible temperature were selected for the study of viral maturation. Of these, 3 mutants which complement each other genetically were used. Two major proteins the nucleocapsid and membrane proteins located, respectively, in the viral nucleoid and membrane were found in intact virions. In cells infected with wild-type Sindbis virus, 4 distinct types of viral RNA with sedimentation coefficients of 40S, 26S, 20S, and 15S were detected in constant distribution. The 20S RNA was RNase-resis-tant, whereas the other types were RNase-sensitive. The 40S RNA, identical to that obtained from the virion, was found associated with nucleocapsid protein as a subviral particle, which was assumed to be the nucleoid. Viral materials from cells infected with the mutants under nonpermissive conditions were compared with those from cells infected with wild-type virus in terms of the distribution of the different types of RNA, the association of infectious viral RNA into subviral particles and the ability of infected cells to hemadsorb goose erythro-cytes. According to these criteria, each of the 3 mutants demonstrated different maturation defects. Defective nucleocapsid proteins and membrane proteins may each account for one of the above mutants. The 3rd mutant may have defects in a minor structural protein or possibly a maturation protein which is involved in the assembly of Sindbis virus.