Electron microscopy of Rous sarcoma virus genome RNA and its heat-dissociated subunits

Native and heat-treated RNAs from the purified Schmidt-Ruppin strain of Rous sarcoma virus (RSV) were fractionated by sucrose density gradients in the presence of ribonuclease inhibitor diethyl-pyrocarbonate and observed by electron microscopy. The structure of native 60-70S RNA was classified into two forms: tanglefolded type and linear type. In the tangle-folded type double stranded portions were observed in several sites. A high frequency of 60-70S RNA were 1.0 mum and 3-3.5 mum in length. Molecules with length about 9mum were of the tangle-folded type while molecules shorter than 6 mum were of the linear form. The structure of heat-treated RNA(30-40S) was linear with the most frequent length being 1-1.5 mum. These results indicate that native 60-70S RNA is folded with the total molecular length being in the order of 6 to 9 mum. Molecules about 3mum long are likely to be the main subunits of 60-70S RNA, and they are fragmented further into smaller subunits of about 1 mum length.