Printed in Great Britain 297 Production of Infectious RNA and Serum-blocking Antigen by Poliovirus Temperature-sensitive Mutants

Poliovirus ts mutants were cultivatcd at a tcmperature (39.6 °) too high for their optimal growth but low enough to pcrmit full growth of the parental is+ strain. Tests for production of infectious RNA and serum-blocking anti-gcn showed a gradient of mutant productivity that corrcspondcd closely with an earlier physiological classification of these mutants. No mutant produced fully wild-type yields of either RNA or antigen. In general, group A mutants produced thc least RNA and antigcn (some yields being undetectable or < i % of ts ÷ values) while group D mutants produced the most (up to 88 % of ts+ RNA and 27"6 % of ts + antigen). Mutants of groups B and C produced intermediate yields. Six of the mutants (all that were classified belonging to groups A or B) convcrtcd thcir small yield of RNA and antigcn to infective virus with an efficiency not significantly different from that of wild-type virus. The rcmaindcr (thirteen mutants, most of those classified belonging to groups C or D) matured either or both their RNA and antigcn incfficicntly and accordingly cxhibitcd a dcfcct in some stagc of maturation or asscmbly