The intergrated proviral genome of the avian carcinoma virus, MH2, has been molecularly cloned and its nucleotide sequence has been determined. Our data indicate that MH2 contains two potential transforming genes: gag-mht and myc. In order to determine which role each potential onc gene of MH2 plays in oncogenesis, we have constructed deletion and frameshift mutants of each of the two MH2 genes, and have tested these mutants for their virus production and transformin function in cultured primary chicken quail cells. We have found that the myc gene transforms primary cells by itsef without the second potential onc gene, and that the gag-mht gene is without detectable transforming function in the primary cell assay. However, futher work is necessary to determine whether the gag-mht gene has a role in oncogenesis in the animal. In order to understand the molecular mechanisms involved in the transduction of cellular mht gense (c-mht) into the MH2 virous, we have moleculary cloned the chicken c-mht from a phage lambda library containing genomic chicken sequences. Nucleic acid hyrbidization abd heteroduplex and DNA sequence analyses indicate that the v-mht sequence captured by the MH2 virus is spead over 25 kilobases (kb) of chicken genomic DNA. The c-mht loucs contains 11 exons which are homologous to the v-hmt sequence. Thus the v-mht onc gene is a subset of its normal cellular homolog in that it lacks introns, and possibly lacks 5' coding sequences. Because there is no sequence homology between c-mht and retoviral helper sequences, the viral transduction of the cellular mht gene occurred thorugh recombination. Finally, we have the temperature-inducible bacterial expression vector developed in our laboratory to express large amount of the v-mht protein. Purification of antibodies against the bacterially-synthesized mht protein is in progress.
