Properties of 42 S and 26 S Sindbis Viral Ribonucleic Acid Species

Two species of ribonuclease-sensitive Sindbis viral ribonucleic acids which sedimented at 42S and 26S were studied. 42S RNA, derived either from virions or from viral nucleoids extracted from infected cultures, was converted by heating to an RNA which sedimented at 26S. The sedimentation patterns of 42S RNA and "derived" 26S RNA were similarly affected in low ionic strength buffers. 42S RNA ran as a homogeneous fraction on polyacrylamide gels; the "derived" 26S RNA as well as "natural" 26S RNA from infected cultures showed similar electrophoretic patterns of heterogeneity. A doubling of 3' polynucleotide termini was observed when 42S RNA was heated. Two possibilities concerning the structure of 42S RNA are considered. (i) It may consist of an aggregate of subunits, joined by means of hydrogen bonds to form a complex molecule. (ii) A heat-labile covalent bond of unknown type may link viral RNA subunits. Although 26S RNA from infected cultures and "derived" 26S RNA from 42S RNA behaved in a similar qualitative manner on gels, their sedimentation characteristics were affected differently in low ionic strength buffers. "Natural" and "derived" 26S RNA appear to consist of a population of fragments. and their behavior in gradients and in gels is probably dictated by the experimental conditions of the analytical methods used.