Avian acute leukemia virus OK10 has an 8.2-kilobase genome and modified glycoprotein gp 78

Two autonomous myc oncogenes in avian carcinoma virus OK10

The oncogenic avian retrovirus OK10 has the genetic structure gag-delta pol-myc-delta-env. The myc sequence is transduced from a cellular gene, proto-myc, while gag, pol, and env are essential retrovirus genes. By analogy with other directly oncogenic retroviruses, the specific myc sequence of OK10 is thought to be essential for transforming function. However, unlike the specific sequences of all other transforming retroviruses that encode unique transforming proteins, the myc sequence of OK10 encodes two potential transforming proteins, p58 and p200. p200 is translated from the gag-delta pol-myc region of genomic RNA, while p58 is thought to be translated from the gag leader and the open reading frame of myc via a subgenomic mRNA. In this paper, we ask whether both myc genes of OK10 are autonomous transforming genes. By differentially inactivating the p200 myc gene of OK10 provirus in vitro and analyzing transforming function in quail embryo cells, it was found that mutants expressing only p58 transformed like wild-type OK10. Further, it was shown that p58 with and without the gag leader had transforming function and that p58 of wild-type OK10 is initiated from the gag leader. Mutants expressing only p200 were also transforming but less efficiently than mutants that express only p58. A mutant OK10 virus in which the native frameshift of retroviruses between gag and pol was deleted expressed a shortened p200 (delta p200). Although this virus expressed more delta p200 than wild-type OK10 did, it transformed cells less efficiently. It follows that OK10 expresses two autonomous transforming genes, which is unique among retroviruses with onc genes.

Avian acute leukemia virus OK 10: analysis of its myc oncogene by molecular cloning

Several DNAs representing the genome of the avian acute leukemia virus OK 10 were isolated by molecular cloning from a transformed quail cell line, 9C, which contained at least six OK 10 proviruses. Recombinant lambda phages harboring the OK 10 genome and additional flanking cellular DNA sequences were studied by restriction endonuclease mapping and hybridization to viral cDNA probes. Six of the clones represented complete proviruses with similar, if not identical, viral sequences integrated at different positions in the host DNA. The organization of the OK 10 genome was determined by electron-microscopic analysis of heteroduplexes formed between the cloned OK 10 DNA and DNAs representing the c-myc gene and the genomes of two other avian retroviruses, Rous-associated virus-1 and MC29. The results indicated that the OK 10 proviral DNA is about 7.5 kilobases in size with the following structure: 5'-LTR-gag-delta polmyc-delta env-LTR-3', where LTR indicates a long terminal repeat. The oncogene of OK 10, v-mycOK 10, forms a continuous DNA segment of around 1.7 kilobases between pol and env. It is similar in structure and length to the v-myc gene of MC29, as demonstrated by restriction endonuclease and heteroduplex analyses. Two of the OK 10 proviruses were tested in transfection experiments: both DNAs gave rise to virus with the transforming capacities of OK 10 when Rous-associated virus-1 was used to provide helper virus functions.

Induction of avidin in chickens infected with the acute leukemia virus OK 10

The presence of avidin, a progesterone-dependent oviductal glycoprotein, was studied in viral tumors. Newborn chickens were infected with the acute leukemia virus OK 10, and the first tumors occurred within 2-3 weeks. Avidin was assayed using a [14C]biotin-binding method and radioimmunoassay. In the control chickens, avidin concentrations were less than 0.3 microgram/g in the plasma and less than 1.5 microgram/g in various tissues including the immature oviduct. In the OK 10 virus-infected chickens, no significant induction was observed during the acute infection or any time thereafter if no tumors were seen. In chickens that developed tumors, avidin concentrations were significantly increased in tumorous tissue only located in the mesenterium and occasionally in the oviduct. In tumors occurring elsewhere (kidney, ovary, muscle, testis, liver, colon) avidin concentrations were not elevated. Tumor-associated avidin had extraordinary biotin-binding capacity after treatment at +90 degrees C similar to the progesterone-dependent avidin, whereas antibody-binding properties suggested that tumor-associated avidin may have a somewhat altered antigenic structure.