Nucleotide sequence of avian carcinoma virus MH2: two potential onc genes, one related to avian virus MC29 and the other related to murine sarcoma virus 3611.

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Abstract
The 5.2-kilobase (kb) RNA genome of avian carcinoma virus MH2 has the genetic structure 5''-.DELTA.gag (0.2 kb)-mht (1.2 kb)-myc (1.4 kb)-c (0.4 kb)-poly(A) (0.2 kb)-3''. .DELTA.gag is a partial retroviral core protein gene, mht and myc are cell-derived MH2-specific sequences, and c is the 3''-terminal retroviral vector sequence. The nucleotide sequence of 3.5 kb from the 3'' end of .DELTA.gag to the 3'' end of molecularly cloned proviral MH2 DNA was determined in order to elucidate the genetic structure of the virus and it was compared with other mht- and myc-containing oncogenic viruses as well as with the chicken proto-myc gene. The following results were obtained. .DELTA.gag-mht forms a hybrid gene with a contiguous reading frame of 2682 nucleotides that terminates with a stop codon near the 3'' end of mht. The 3'' 969 nucleotides of mht up to the stop codon are 80% sequence related to the onc-specific raf sequence of murine sarcoma virus 3611 (94% homologous at the deduced amino acid level). The myc sequence is preceded by an RNA splice acceptor site shared with the cellular proto-myc gene, beyond which it is colinear up to a 3''-termination codon and 40 noncoding nucleotides with the myc sequences of avian retrovirus MC29 and chicken proto-myc. Thus, myc forms, together with a 5'' retroviral exon, a second MH2-specific gene. myc is followed by the 3''-terminal c region of .apprx. 400 nucleotides, which is colinear with that of Rous sarcoma virus except for a substitution near the 5'' end of the long terminal repeat. It is concluded that MH2 contains 2 genes with oncogenic potential, the .DELTA.gag-mht gene, which is closely related to the .DELTA.gag-raf transforming gene of MSV 3611, and the myc gene, which is related to the transforming gene of MC29. Evidently, the cellular proto-onc genes, which on sequence transduction become viral onc genes, are a small group because among the 19 known onc sequences, 5 are shared by different taxonomic groups of viruses of which the mht/raf homology is the closest determined so far.