Expression of C-type virus in non differentiating rat myoblasts correlates with neoplastic progression.

Analyses of intracellular RNAs and proteins, measurements of reverse transcriptase activity and electron microscopy showed that non transformed L6 alpha 1 rat myogenic cells produce no endogenous C-type virus whereas two non fusing variants, the low malignant M4 cell and high malignant RMS4 cell produce small and large amounts of virus respectively consistent with different levels of intracellular viral transcripts. Two non viral transcripts bearing LTR sequences are present in M4 and RMS4 cells and absent from L6 alpha 1 cells although the 3 cell lines exhibit strictly similar patterns of C-type proviral genes.