Cells infected with ts mutants of poliovirus were incubated at temperatures (39.4 °-39.6 °) too high to support full production of infective virus, and were then examined for certain changes that are normally characteristic of virus growth. The changes reported here, which can be used as genetic characters of the virus, are denoted:-a+: the production of poliovirus antigen; pti+: the prevention of cellular incorporation of thymidine; ppi1+, ppi2+, ppi3+: the prevention of 32P incorporation into, respectively, 28 S, 16 S or 4-10 S cellular RNA. The wild-type strain (ts+) grew well at 39.6 °; it also displayed all five characters at 39.6 °, but most of the 29 mutants tested did not. Tests for the characters a+, pti+, and ppi3+ revealed large temperature defects in many mutants, and were used to define four groups of mutants with the following combinations of characters: group A: a, ppi3, pti; group B: a, ppi3; group C: a; group D: all characters wild type. Other combinations were not found, and so these characters covary in an asymmetrical or polar fashion. Temperature shift experiments suggested that certain gene products are made and used throughout the growth cycle, although most appear to be associated with 'late' junctions.
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