Specific RNA sequences and gene products of MC29 avian acute leukemia virus

Abstract

The 28S RNA of the defective avian acute leukemia virus MC29 contains two sets of sequences: 60% are hybridized by DNA complementary to other avian tumor virus RNAs (group-specific cDNA) and 40% are hybridized only by MC29-specific cDNA. Specific and group-specific sequences of viral RNA, defined in terms of their large RNase TI-resistant oligonucleotides, were located on a map of all large T, oligonucleotides of viral RNA. Oligonucleotides representing MC2-specific sequences of viral RNAmnapped between 0.4 and 0.7 unit from the 3'-poly(A) end. Oligonucleotides of groupspecific sequences mapped between 0 and 0.4 and between 0.7 add I map unit. Cell-free translation of viral RNA yielded three proteins with approximate molecular weights of 120,000,356,000, and 37,000, termed P120me P5i, and P37mc. P120me contained both MC29specific peptiies and serological determinants and peptides of the conserved, internal group-specific antigens of avian tumor viruses. P120me is translated only from ful~length 28S RNA. Furthermore, MC29 RNA contains sequences related to the groupspecific antigen gene (gag), near the 5' end, which are folowed by MC29specific sequences. We conclude that this protein is translated from the 5' 60% of the RNA, and that it includes a segment translated from the specific sequences. It is suggested that the transforming (onc) gene of MC29 may consists of the specific and some group-specific RNA sequences and that Pl2rnc, which is also found in transformed cells, may be the onc gene product. MC29 is an avian RNA tumor virus that causes acute leukemia and carcinoma and also transforms fibroblasts in culture (1-4). The transforming or onc (5) gene of MC29 has not been defined genetically or biochemically. The viral genome is a 28S RNA (5700 nucleotides) that is identified as being MC29-specific by its absence from pure helper virus and because the sequence of 28S RNA is conserved when propagated with different helper viruses (6)(7)(8) However, if the specific sequences of MC29 are contiguous and if they code for a specific protein, they are candidates for a MC29 onc gene analogous to the src gene of RSV. Therefore we identified and located the MC29-specific sequences on the viral 28S RNA and then investigated the proteins encoded by these sequences. Preliminary work has been described recently (8). RESULTSMapping MC29-Specific and Group-Specific Sequences of MC29 RNA. Due to its defectiveness, MC29 virus can only be propagated in the presence of a helper virus. The helper virus used here was ring-neck pheasant virus (RPV) (4). The 50-70S RNA extracted from a mixture of MC29 and its helper contains two distinct monomer RNA species, a 34S helper virus RNA and a 28S MC29 RNA (6). The 28S MC29 RNA has been electrophoretically isolated and its RNase T1-resistant oligonucleotides have been analyzed by fingerprinting (Fig. 1A). The compositions, of the RNase A-resistant fragments of each oligonucleotide have been reported (6-8) and were extended and revised here as described in the legend of Fig. 1. To ...

Avian acute leukemia viruses MC29 and MH2 share specific RNA sequences: Evidence for a second class of transforming genes

“…This sequence maps between 2.5 and 4 kb from the 3' end of MC29 RNA and codes together with other sequences of viral RNA for a MC29-specific, nonstructural protein of 120,000 daltons (9) that is also expressed in transformed cells (4). Therefore, it was suggested that this sequence is a candidate for the onc gene of MC29 (9).…”

“…This sequence maps between 2.5 and 4 kb from the 3' end of MC29 RNA and codes together with other sequences of viral RNA for a MC29-specific, nonstructural protein of 120,000 daltons (9) that is also expressed in transformed cells (4). Therefore, it was suggested that this sequence is a candidate for the onc gene of MC29 (9).A definitive identification of the onc genes of MC29 and MH2 is complicated by the defectiveness of these viruses in all three replicative genes of avian tumor viruses (3-5, 10, 11). It is impractical to detect onc deletion mutants, a capability that proved essential for the definition of the src gene of Rous sarcoma virus (RSV) (12-16), because onc deletions of MH2 or MC29 would lack detectable biological markers of any viral gene.…”

“…However, the genome of MC29, which is 5.7 kilobases (kb), was shown to contain a specific sequence of about 1.5 kb that is unrelated to the replicative genes of avian tumor viruses and is also unrelated to the conserved src genes, which are the onc genes of avian sarcoma viruses (8,9). This sequence maps between 2.5 and 4 kb from the 3' end of MC29 RNA and codes together with other sequences of viral RNA for a MC29-specific, nonstructural protein of 120,000 daltons (9) that is also expressed in transformed cells (4).…”

“…A recombination analysis, which proved useful in defining the src gene of RSV (17,18), is also complicated by the functional defectiveness of MC29 and MH2 in all three replicative genes. Recombinants would lack readily detectable markers, and specific sequences such as those found in MC29 (9) would not be expected to recombine with other avian tumor viruses lacking them (19).…”

Avian leukaemia viruses and haematopoietic cell differentiation

“…These proteins seem to be fusion proteins between part or all of the gag gene product (specifying viral core proteins) and a unique portion which is similar in viruses with similar biological specificity only (Kitchener & Hayman, in press). This, in addition to the co-linearity of the unique ("transforming") sequences in the RNA of AEV and MC29 with the corresponding fusion proteins (Kitchener & Hayman, in press;Mellon et al, 1978;Lai et al, 1979) suggests that they represent the transforming proteins of DLVs.…”