St. Louis encephalitis virus temperature-sensitive mutants. I. Induction, isolation and preliminary characterization.

Nine temperature-sensitive (ts) mutants of St. Louis encephalitis virus were isolated after "forced mutagenesis" with 5-fluorouracil or 5-azacytidine. The ts mutants could be grouped on the basis of RNA synthesis at 40 degrees C, the nonpermissive temperature and complementation analysis. Four complementation groups were identified. Members of two of the groups were negative for RNA synthesis at 40 degrees C while the remainder were positive.