Two different types of transcription for the myelocytomatosis viruses MH2 and CMII.

Abstract

The four avian defective leukemia retroviruses (DLVs) MC29, CMII, MH2 and OK10 all transform primarily 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. We show here that MH2 virus does not conform to this model. Whereas MC29 produces only one mRNA detectable by RNA blotting in productively transformed cells, we reported recently that OK10 induced the synthesis of two myc‐containing mRNAs, the smaller species being a spliced mRNA and a possible candidate for a transforming protein lacking gag determinants. However, the studies with OK10 were ambiguous because this virus produced also, in infected cells, a fusion protein containing gag, pol and myc determinants. We have therefore investigated the transcription pattern of the two other members of this group of viruses, namely CMII and MH2. Our results show that CMII resembles MC29 whereas MH2 produces, as OK10, two mRNAs containing myc‐related sequences. However, unlike OK10, the MH2 fusion protein of 100 kd described previously cannot contain myc determinants and thus is likely to produce from its subgenomic mRNA a v‐myc protein‐lacking gag determinants. We thus conclude that the product of the v‐myc oncogene is transforming with (MC29) or without (MH2) its fusion to gag determinants and that the multiple oncogenic spectrum is not basically affected since MH2 and MC29 both transform macrophages, fibroblasts and epithelial cells.

Multiple domains for the chicken cellular sequences homologous to the v-ets oncogene of the E26 retrovirus.

“…High-molecular-weight chicken DNA was prepared from total embryos as previously described (23). Plasmid DNA and recombinant phage DNAs were prepared as described previously (22).…”

“…Fragments representative of the viral env gene were derived from the Prague A strain of Rous sarcoma virus (Pr-RSVA) genome as illustrated by Saule et al (22). These fragments were labeled by nick-translation with New England Nuclear Corp. nick translation kits.…”

“…Hybridization of blots to 32P-labeled DNA, washing, and autoradiography at -70°C with Kodak X-ray films and Du Pont Lightning-Plus X-ray intensifying screens were performed as described previously (22).…”

Mutagenesis of avian carcinoma virus MH2: only one of two potential transforming genes (delta gag-myc) transforms fibroblasts.

“…This gene includes a gag-derived 5' exon of only six gag codons (therefore 8gag) and a 3' 1.6-kb myc exon that is colinear with the two 3'-terminal exons of chicken proto-myc (5,14). This gene is expressed via a subgenomic 2.6-kb mRNA as a 57,000-dalton (p57) protein product (15)(16)(17)(18). The 7.5-kb RNA genome of OK10 virus (19) contains two overlapping myc-related genes (7); a contiguous gag-Apol-myc gene, which encodes a p200 protein; and a discontiguous 8gag-myc gene, which as in MH2 is also expressed as a subgenomic 3.5-kb mRNA encoding a p57 protein (6,17,18).…”

Avian carcinoma virus MH2 contains a transformation-specific sequence, mht, and shares the myc sequence with MC29, CMII, and OK10 viruses.

“…Because MH2 also encodes a gag-related protein of similar size, p100 (7), it was assumed that the MH2 p100 protein was a structural homolog of the MC29 transforming protein. Nevertheless, recent analyses have suggested that the p100 protein is not serologically related to the-myc portion of the p110 protein of MC29 (unpublished data) and that the myc sequence of MH2 may be expressed via a subgenomic mRNA (13,14) to encode a 57-kDa protein (13 Linial (8,13).…”