2 DIFFERENT TYPES OF TRANSCRIPTION FOR THE MYELOCYTOMATOSIS VIRUSES MH-2 AND CM-II

The 4 avian defective leukemia retroviruses (DLV) MC29, CMII, MH2 and OK10 all transform primarily chicken macrophages in an in vitro bone marrow transformation assay, and contain specific nucleotide sequences closely related to the myc gene of MC29. These viruses were thought to express their oncogenic potential through a gag-myc fusion polyprotein, since fusion polyproteins were found in all tested cells transformed by MC29. MH2 virus does not conform to this model. Whereas MC29 produces only 1 mRNA detectable by RNA blotting in productively transformed cells. OK10 induced the synthesis of 2 myc-containing mRNA, the smaller species being a spliced mRNA and a possible candidate for a transforming protein lacking gag determinants. The studies with OK10 were ambiguous because this virus produced also, in infected cells, a fusion protein containing gag, pol and myc determinants. The transcription pattern of the 2 other members of this group of viruses, namely CMII and MH2 were studied. CMII resembles MC29 whereas MH2 produces, as OK10, 2 mRNA containing myc-related sequences. Unlike OK10, the MH2 fusion protein of 100 kilodalton described previously cannot contain myc determinants and thus is likely to produce from its subgenomic mRNA a v-myc protein-lacking gag determinants. Evidently, the product of the v-myc oncogene is transforming with (MC29) or without (MH2) its fusion to gag determinants, and the multiple oncogenic spectrum is not basically affected since MH2 and MC29 both transform macrophages, fibroblasts and epithelial cells.