Nucleotide sequence analysis of the proviral genome of avian myelocytomatosis virus (MC29).

Abstract

The nucleotide sequence of the integrated proviral genome of avian myelocytomatosis virus (MC29) coding for gag-myc protein has been determined. By comparison of this nucleotide sequence with the helper virus as well as the c-myc region, it was possible to localize the junction points between helper viral and v-myc sequences. These studies demonstrate that (i) the large terminal repeat sequence of MC29 is very similar to that of Rous sarcoma virus, (ii) the viral genome has suffered extensive deletions in the gag, pol, and env genes, (iii) the gag region can code for p19, plO, and part of p27, (iv) the recombination between viral and cellular sequences occurred in the coding region of p27 such that the open reading frame extends for an additional stretch of 1,266 base pairs, resulting in a gag-myc hybrid protein, (v) the open reading frame terminated within the v-myc region 300 bases upstream of v-myc-helper viral junction, and (vi) the v-myc helperviral junction at the 3' end occurred in the middle of env gene, rendering it defective.Myelocytomatosis virus (MC29) is a replication-defective avian retrovirus that induces a broad spectrum of malignant diseases, including myelocytomas, renal and liver tumors, and, less typically, carcinomas, sarcomas, and erythroblastosis (1, 2). The same virus induces morphological transformation of fibroblasts, epithelial cells, and macrophages in culture (3)(4)(5). This virus arose by recombination of the nondefective helper virus (MC29-associated virus) and cellular sequences present within the normal chicken genome. These latter sequences termed "myc" appear to code for the transforming properties of the virus (6-8). The 5.7-kilobase (kb) RNA of MC29 has been shown to contain 1.6 kb of myc sequences that are flanked by partial Agag gene at the 5' end and Aenv gene at the 3' end (6). Nonproducer quail cell lines transformed by MC29 contain a 110,000-dalton protein with viral antigenic determinants (9). This protein appears to be a hybrid protein, the amino-terminal region of which is composed of helper virus gag gene products. The development of molecular cloning and DNA sequence analysis techniques has made the detailed analysis of the virus genome structure possible. In an attempt to better understand the structural organization and possible molecular mechanisms involved in transformation by MC29, we have undertaken primary DNA sequence analysis of the molecularly cloned integrated viral genome. Putative regulatory signals for transcription and translation of v-myc sequences have been identified. Sequence analysis has also demonstrated the occurrence of a long open reading frame within v-myc region that could code for the MC29 transforming protein.MATERIALS AND METHODS Molecular Cloning. The integrated proviral genome of MC29 was initially cloned in Agt WES-AB (10). In the present studies, two subclones of this DNA fragment were utilized for sequence analysis. A 1.4-kilobase-pair (kbp) Xho I fragment that contained the 5' large terminal repeat (LTR) and gag sequences...

The v-myc oncogene

“…Several substitution mutations are observed among vMyc proteins that di er from that of c-Myc (one for CMII, two for OK10, 27 for MH2, three for FTT with two deletions at C-terminus, and ®ve or seven for MC29 depending on the isolate) (Alitalo et al, 1983;Doggett et al, 1989;Hay¯ick et al, 1985;Kan et al, 1984;Reddy et al, 1983;Walther et al, 1985;Watson et al, 1983). Most of the mutations occur in the Nand C-termini of v-Myc, mapping to the domains required for transformation.…”

“…This virus was also found to cause endotheliomas, sarcomas as well as liver and kidney carcinomas (Table 1). Following the advent of recombinant DNA techniques, the viral genome was cloned and the sequence of the v-myc gene was elucidated (Alitalo et al, 1983;Reddy et al, 1983;Watson et al, 1983). Later, the v-myc sequence was found to occur in four other independent retroviral isolates CMII, MH2, OK10 and FTT (Doggett et al, 1989;Hay¯ick et al, 1985;Kan et al, 1984;Walther et al, 1985), which cause di erent neoplastic diseases in their hosts (Table 1).…”

Neural Stem/Progenitor Cell Clones as Models for Neural Development and Transplantation

“…The critical function domains of Myc proteins have been mapped to their N-and Cterminus, which contain the transregulatory domain and the basic-helix-loop-helix-leucine zipper (bHLH/LZ) domain, respectively (Farina et al, 1992;Min et al, 1993;Min and Taparowsky, 1992). www.intechopen.com V-Myc, the viral homologue of cellular Myc (c-Myc), was first discovered from a transforming retrovirus MC29 from chicken with spontaneous myelocytomatosis and subsequently cloned and sequenced (Alitalo et al, 1983;Reddy et al, 1983;Watson et al, 1983). V-Myc is expressed as a fusion protein Gag-Myc in MC29 and other related retroviruses.…”

What retroviruses teach us about the involvement of c-Myc in leukemias and lymphomas

“…Transduction of cMyc was initially recognized in the retrovirus MC29, leading to the synthesis of a 110 kDa fusion product of Myc with a viral capsid protein precursor, Gag (called Gag-Myc). 47 Because the Gag-Myc fusion product (also called v-Myc) is synthesized from the retroviral promoter, which is considerably stronger than the c-Myc promoters, 48 the concentration of the fusion protein is greatly increased inside infected cells. In addition, during transduction and selection of the hybrid retrovirus, v-Myc sustained a point mutation at threonine-61 (Thr-61) that led to the stabilization of the fusion protein.…”