Size, subunit composition, and secondary structure of the Friend virus genome

Electron microscope and gel electrophoresis studies show that the high molecular weight (50 to 70S) RNA extracted from Friend virus (FV) is a dimer with the same basic structure previously observed for the RNAs from RD 114 virus, baboon virus, and woolly monkey virus. This observation greatly strengthens the inference that the dimer structure is a general characteristic of the RNAs of all mammalian type C viruses. The FV dimer is slightly less stable than the RNA dimer of woolly monkey virus, which is, in turn, much less stable than those of RD 114 and baboon virus. There are three FV monomer components, small (S), medium (M), and large (L), with molecular lengths of 6.7 ± 0.6, 7.7 ± 0.6, and 9.5 ± 0.6 kilobases, respectively. There are approximately equal amounts of the S and M components and much less of the L component. Most of the dimers are homodimers (SS, MM, and LL). The frequency of heterodimers (SM, SL, ML) is much less than expected for a random assortment model.