Polynucleotide sequence homologies among polioviruses.

Measurements of polynucleotide sequence homologies have proved useful in investigating the relationships of viruses, bacteria, plants, and animals.The techniques have largely been restricted to examination of organisms whose ge- netic information is contained in double-stranded DNA.With few exceptions, the nucleic acids of mature RNA virions are single-stranded and therefore not ame- nable to hybridization.It has become clear, however, that cells infected with RNA viruses also contain RNA's that are base-paired and consist of "plus" strands (indistinguishable from encapsidated viral RNA) and complementary, or "minus," strands.1-3Recently described methods for the extraction and purifi- cation4 of this ± RNA now provide minus strands that permit examination of RNA-RNA interactions.This paper describes polynucleotide sequence homologies among the RNA's of polioviruses types 1, 2, and 3.The method employed was to react radio- labeled, DMSO "melted" + -RNA with a large excess of +RNA prepared from either homologous or heterologous purified poliovirus.The degree of double- strand reformation of the heterologous compared with the homologous reaction was taken as a measure of the extent of polynucleotide sequences shared among the encapsidated viral RNA's.Materials and Methods.-Viruses and immune sera: Polioviruses type 1 (Brunhilde) and type 3 (Leon) were obtained from the Research Reference Reagents Branch of the National Institutes of Health, as were monkey hyperimmune sera to these strains and to poliovirus type 2 (Lansing).Polioviruses type 1 (Mahoney) and type 2 (MEF1) were provided by Dr. Paul Gerber, Division of Biologics Standards.Infectivity assays and neutralization tests: Infectivity of virus stocks for HeLai cell monolayers was measured by the plaque method of Holland and McLaren.6 Neutraliza- tion tests were effected by incubating 50 PFU of virus with serial dilutions of immune serum in phosphate-buffered saline, pH 7.6, for 60 min at 370C.A plaque reduction of 80% was taken as neutralization end point.