Structure of 50 to 70S RNA from Moloney sarcoma viruses.

The 50 to 70S RNAs of two clonal isolates of defective Moloney sarcoma-leukemia helper virus complex were analyzed by gel electrophoresis and electron microscopy. The RNAs extracted from both clone 3 and clone 124-5R of Moloney sarcoma-leukemia virus complex contained some large monomer subunits ca. 10,000 nucleotides in length (10 kilobases), which are believed to be the Moloney leukemia virus subunits. Both RNAs had an excess of a smaller, sarcoma-specific subunit, 5 kilobases (clone 3) or 6 kilobases (clone 124-5R) in length. Electron microscopy of intact 50 to 70S dimer RNA molecules showed for both clones many dimers of two small subunits, some dimers of two large subunits, but few if any heterodimers with one large and one small subunit. This result was unexpected because the sequences near the 5'end of the RNA subunits, which are believed to be involved in the dimer linkage, are probably homologous between the large and small subunits. We also observed that some small-small dimers migrated anomalously slowly on nondenaturing gels. The nature of this slow-migrating complex is unkown; it could be a higher aggregate of the small-small dimer with additional small or large subunits, or it could be an extended conformation of the small-small dimer.