Properties of Visna Virus Particles Harvested at Short Time Intervals: RNA Content, Infectivity, and Ultrastructure

Abstract

The major RNA component of Visna virus harvested at short intervals of time (5 min) is not the 60 to 70 S RNA but a molecule of higher electrophoretic mobility. This RNA has been isolated and characterized. Its sedimentation coefficient is identical to that of 30 to 40 S RNA subunits obtained by heat denaturation of the 60 to 70 S RNA. In 1.8% acrylamide gels without agarose the electrophoretic mobility of 30 to 40 S RNA subunits present in rapidly harvested virus is slightly lower than that of the subunits obtained by denaturation of the 60 to 70 S RNA; after heat denaturation the mobilities are identical. These free RNA subunits present in early virus particles assemble into a 60 to 70 S RNA complex as shown by following the RNA content of early virus incubated at 37 C for various lengths of time. The rate of this maturation process is slow. There is no difference between the infectivity of immature and mature virus particles. Both particles have a dense core when examined in sections of virus pellets.