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

Abstract

Avian carcinoma virus MH2 has been grouped together with MC29, CMII, and OK10, because all of these viruses share a transformation-specific sequence termed myc. A 5.2-kilobase (kb) DNA provirus of MH2 has been molecularly cloned. The complete genetic structure of MH2 is 5'-delta gag(1.9-kb)-mht(1.2-kb)-myc(1.3-kb)-delta env(?) and noncoding c-region (0.2-kb)-3'. delta gag, delta env, and c are genetic elements shared with nondefective retroviruses, whereas mht is a unique, possibly MH2 transformation-specific, sequence. Hybridizations with normal chicken DNA and cloned chicken c-myc DNA indicate that the mht sequence probably derives from a normal cellular gene that is distinct from the c-myc gene. The genetic structure of MH2 suggests that the delta gag and mht sequences function as a hybrid gene that encodes the p100 putative transforming protein. The myc sequence of MH2 appears to encode a second transforming function. Therefore, it seems that MH2 contains two genes with possible oncogenic function, whereas MC29, CMII, and OK10 each carries a single hybrid delta gag-myc transforming gene. It is remarkable that, despite these fundamental differences in their primary structures and mechanisms of gene expression, MH2 and MC29 have very similar oncogenic properties.

Cellular oncogenes (c-erb-A and c-erb-B) located on different chicken chromosomes can be transduced into the same retroviral genome.

“…The transduction of more than one cellular gene into a single retrovirus is a relatively common event, in contrast to the previous belief: transduction of c-erb-A and c-erb-B gave rise to two strains of AEV, ES4 and R, isolated independently in the past (8), and both the MH-2 (11,12) and E26 (14, 16) a 8 9 10 11 12 13 14 15 16 17 18 19 20 (Fig. 1).…”

“…It has been suggested that these discrepancies arise from the fact that the MSB-1 cell line generally used for fractionation of chicken chromosomes (15,17) Bishop, unpublished data). It therefore appears safe to conclude that in chickens, as in other species (4), cellular oncogenes are dispersed among multiple chromosomes and that on several occasions two of these dispersed genes, c-erb-A and c-erb-B (29), c-myc and c-mil (also termed c-mht) (11,12), or c-mvb and c-ets (14,16), have been transduced into the genome of a single retrovirus.…”

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

“…However, three oncogenic retroviruses contain two genes with oncogenic potential, namely the avian carcinoma viruses MH2 (2-5) and OK10 (6, 7) and avian erythroblastosis virus (AEV) (8,9). The 5.5-kilobase (kb) RNA genome of MH2 (10) has the genetic structure Agag-mht-myc (2)(3)(4)(5). One of the two genes with potential transforming function encoded by MH2 is a 3-kb Agag-mht gene, defined by a p100 protein product (11).…”

c-Myc-Induced Genomic Instability

“…Avian leukosis virus-induced bursal lymphomas were first reported by Ellerman and Bang (1908). Subsequently, a series of avian retroviruses, including MH2, OK10, MH29, and CMII (Duesberg and Vogt 1979;Bister and Duesberg 1980), were isolated and found to contain MYC sequences (Chiswell et al 1981;Bunte et al 1983;Hann et al 1983;Kan et al 1983; Thompson et al 1987). The name MYC originated from "myelocytomatosis," which consists of avian leukosis (hematopoietic neoplasm) and sarcomas.…”