Specific Sindbis virus-coded function for minus-strand RNA synthesis

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Abstract
The synthesis of minus-strand RNA was studied in [chicken embryo fibroblast] cell cultures infected with the heat-resistant strain of Sindbis virus and with temperature-sensitive (ts) mutants belonging to complementation groups A, B, F and G; all exhibited an RNA-negative (RNA-) phenotype when infection was initiated and maintained at 39.degree. C, the nonpermissive temperature. When infected cultures were shifted from 28.degree. C (the permissive temperature) to 39.degree. C at 3 h postinfection, the synthesis of viral minus-strand RNA ceased in cultures infected with ts mutants of complementation groups B and F, but continued in cultures infected with the parental virus and mutants of complementation groups A and G. In cultures infected with ts 11 of complementation group B, the synthesis of viral minus-strand RNA ceased; the synthesis of 42S and 26S plus-strand RNA continued for at least 5 h after the shift of 39.degree. C. When ts11-infected cultures were returned to 28.degree. C 1 h after the shift of 39.degree. C, the synthesis of viral minus-strand RNA resumed and the rate of viral RNA synthesis increased. The recovery of minus-strand synthesis required translation of new proteins. A least 1 viral function apparently is required for alphavirus minus-strand synthesis that is not required for plus-strand synthesis. In cultures infected with ts6 of complementation group F, the syntheses of viral plus-strand and minus-strand RNA were drastically reduced after the shift of 39.degree. C. Since ts6 failed to synthesize plus-strand and minus-strand RNA after the shift to 39.degree. C, at least 1 common viral component appears to be required for the synthesis of both minus-strand and plus-strand RNA.