Electron microscopic studies on the structure of 60-70S RNA of avian myeloblastosis virus.

Structural properties of the 60-70S RNA complex of avian myeloblastosis virus (AMV) were analysed in electron microscope after treatment under a set of non-denaturing, gently and strongly denaturing conditions. By selected denaturing conditions, the significant fraction of 60-70S AMV RNA molecules revealed partially unfolded structures either in a dimer or a more complex form and in a length corresponding to mol. wt. of 5.6 X 10(6). The typical dimers contained a characteristic central structure connecting the subunits and similar to those described for Rous sarcoma virus (RSV) and mammalian retrovirus RNAs. This dimer linkage in the AMV genome occurred at 384 +/- 43 nucleotides from one end of each subunit. Besides partially unfolded complexes, collapsed structures and extended linear molecules were observed. The length of majority of the linear molecules had reached a half of that of the partially unfolded complexes corresponding to the mol. wt. of monomers estimated under conditions of strong denaturation to be 2.8 X 10(6). Based on our findings, we conclude that the genome of AMV shares the dimer structure with RSV and mammalian retroviruses. We also conclude that the secondary structure of AMV RNA molecule is more labile than that of RNA of mammalian retroviruses.