The transforming gene of Moloney murine sarcoma virus

A birds'-eye view of the activity and specificity of the mRNA m6 A methyltransferase complex

Appropriate control of the transcriptome is essential to regulate different aspects of gene expression during development and in response to environmental stimuli. Fast accumulating reports are recognizing and functionally characterizing several types of modifications across transcripts, which have created a new field of RNA study named epitranscriptomics. The most abundant modification found in messenger RNA (mRNA) is N6-methyladenosine (m⁶ A). m⁶ A addition is achieved by a large methyltransferase complex (MTC). The m⁶ A-MTC is composed of the methyltransferases METTL3 and METTL14 as the catalytic core, and several protein factors necessary for its correct catalysis, which include WTAP, RBM15, VIRMA, HAKAI, and ZC3H13. To fully appreciate the relevance of this modification, it is important to dissect the basis for the MTC function as well as to define its interaction with other cellular partners. Here, we summarize previous and recent knowledge on these issues to provide a guide for future research and put forward ideas on the flexibility and specificity of this process. This article is categorized under: RNA Processing > RNA Editing and Modification RNA Interactions with Proteins and Other Molecules > Protein-RNA Recognition.

Detection of Moloney murine sarcoma virus in tissues and cultured cells by the polymerase chain reaction

The polymerase chain reaction was used for Moloney murine sarcoma virus (MoMuSV) detection in frozen and formalin-fixed, paraffin-embedded tissue sections and cultured cells isolated from MoMuSV-induced tumors. Rapid DNA extraction by proteinase K digestion, followed by CHROMA SPIN + TE-100 column purification proved to be satisfactory. Two pairs of overlapping primers, flanking 1026 base pair (bp) to 221 bp, allowed to choose among four different length of DNA-amplified segments. Although net amplification was obtained for frozen tissue and tumor cultured cells in all combinations of primers, the maximum specificity and sensitivity resulted with 602 bp fragment. This product was fully and adequately digestible using Apa I and Sau3A I restriction endonucleases. DNA extracted from paraffin-embedded sections yielded an amplification product only when the primer pair which delineated a 221-bp segment was used. This reproducible method could be useful for diagnostic and for pathogenetic investigations of MoMuSV infections.

Insertional mutations in mammals and mammalian cells

The retroposon sequences, their mechanisms of transposition and the occurrence of insertional mutation in the mammalian genome are reviewed. Insertional mutations fall into two broad categories: those due to the disruption of a gene following the physical integration of a foreign DNA sequence result in loss of gene product and would be expected to be associated with a recessive mutation. A second class of insertional mutation is well documented in which upon integration the promoter/enhancer activities inherent in the retroposon genome exert their influence on neighboring genes. This promoter/enhancer activity of integrated retroposons may have effects over relatively long distances and thus limit the possibilities of establishing an association between retroposon integration and mutation. It is emphasized that a systematic search for insertional mutations in the mammalian genome involves an extensive two-dimensional array of possible retroposon sequences and mutant alleles. Present results represent only a small portion of the total array. Future studies promise to be fruitful in efforts to isolate genes through insertional tagging, to characterize the mechanisms of retroposon transposition, as well as to study the stability of the mammalian genome.

Carboxyl-terminal determinants of Abelson protein important for lymphoma induction

The carboxyl-terminal region of the Abelson protein is not absolutely required for Abelson virus transformation. However, Abelson virus strains encoding proteins missing portions of this region have a reduced ability to transform lymphoid cells in vitro and in vivo. One such strain, called P90A, is unique in that P90A-injected mice almost always develop tumors containing highly oncogenic variants that encode new forms of Abelson protein. In this work, we have examined the mechanism by which these variants are generated and used the variants to identify carboxyl-terminal protein sequences important for the induction of Abelson disease. Analysis of mice injected with helper-free P90A virus stocks demonstrates that the variants are generated during viral replication in vivo, probably as a consequence of error-prone reverse transcription. The sequence of the P90A viral genome reveals that a 19-base deletion is responsible for synthesis of the truncated Abelson protein. As a consequence of this mutation, 167 carboxyl-terminal amino acids normally found in the wild-type protein have been replaced by 33 amino acids derived from an alternative reading frame. Site-directed mutants show that the combination of the deletion and the P90A carboxyl terminus is required for the generation of variants. Thus, the particular structure of the P90A protein, not the specific residues lost or gained, alters the transforming potential of the Abelson protein. Finally, the sequence of the variants encoding smaller Abelson proteins reveals that as few as 452 v-abl-encoded amino acids are required for rapid induction of Abelson disease.

Temperature-sensitive mutants of Abelson murine leukemia virus deficient in protein tyrosine kinase activity

The effect of two missense mutations in abl on transformation by Abelson murine leukemia virus was evaluated. These mutations led to the substitution of a histidine for Tyr-590 and a glycine for Lys-536. Both changes gave rise to strains that were temperature dependent for transformation of both NIH 3T3 cells and lymphoid cells when expressed in the context of a truncated Abelson protein. In the context of the prototype P120 v-abl protein, the Gly-536 substitution generated a host range mutant that induced conditional transformation in lymphoid cells but had only a subtle effect on NIH 3T3 cells. The combination of both substitutions gave rise to a P120 strain that was temperature sensitive for both NIH 3T3 and lymphoid cell transformation. The Abelson proteins encoded by the temperature-sensitive strain displayed in vitro kinase activities that were reduced when compared with those of wild-type proteins. In vivo, levels of phosphotyrosine were reduced only at the restrictive temperature. Analysis of cells expressing either the wild-type P160 v-abl protein or the P210 bcr/abl protein and an Abelson protein encoded by a temperature-sensitive strain failed to correct this defect, suggesting either that tyrosine phosphorylation in vivo is an intramolecular reaction or that the protein encoded by the temperature-sensitive strain is a poor substrate for tyrosine phosphorylation in vivo. These results raise the possibility that tyrosine phosphorylation of Abelson protein plays a role in transformation.

Histopathologic studies on myeloproliferative sarcoma virus (MPSV) induced leukemias and hemangiosarcoma in Jar-2 rats

It is well known that MPSV induces myeloproliferative syndrome (MPS) in mice. Intravenous one shot inoculation of myeloproliferative sarcoma virus (MPSV) with Friend murine leukemia virus (F-MuLV) as a helper in newborn Jar-2 rats (on the second neonatal day) yielded hematopoietic malignancies in all the treated rats (25/25 rats) after 2 weeks' latency. MPS appeared from the 14th day in 14 rats. In the midst of the myeloproliferative field of the spleen and bone marrow, myeloblastic or myeloblastic-erythroblastic foci were observed. From 19th day, acute myeloblastic leukemia occurred in 3 rats and erythroleukemia in 8 rats. MPSV induced first MPS which remained as such or later developed into acute leukemia. Myelofibrosis as seen in mice was not observed. In addition, hemangiosarcoma of the brain, spinal cord and spleen appeared in 15 rats from the 24th day, and were often multiple. MPSV can yield the tumor only in newborn rats, and target cells of MPSV are not only hematopoietic cells but also endothelial cells of the brain, spinal cord and occasionally spleen.

Isolation of temperature-sensitive Abelson virus mutants by site-directed mutagenesis

Mutants of Abelson virus encoding temperature-sensitive protein-tyrosine kinase (EC 2.7.1.112) were created by site-directed mutagenesis using sequence information from temperature-sensitive mutants of the related v-src oncogene. Expression of these two independent mutations in Escherichia coli resulted in reduced phosphorylation of the mutant proteins at high temperature. Viruses containing one of the mutations induced conditional transformation of both NIH 3T3 and lymphoid cells when expressed in the context of a truncated transforming protein. These results underscore the functional homology between protein-tyrosine kinases and suggest that transfer of mutations within a related gene family may provide a rapid method to create mutants.

A temperature-sensitive mutant of the myeloproliferative sarcoma virus, altered by a point mutation in the mos oncogene, has been modified as a selectable retroviral vector

The myeloproliferative sarcoma virus (MPSV) is a mos-oncogenic retrovirus which induces an acute myeloproliferative disease in adult mice. The isolation and molecular cloning of two mutants of MPSV temperature sensitive (ts) for mos transformation (Kollek et al., J. Virol. 50:717-724, 1984) have been described previously. In this report, we describe the biological activity of these clones, the molecular basis of the ts lesion of one clone, and the construction of a selectable vector based on the MPSV ts genome. Both molecular clones, ts159 and ts124, proved to have retained the ts phenotype, the former being tighter for the induction and maintenance of the transformed phenotype. A single transition (G----A) at position 1888 in the mos coding region, resulting in the change of Gly to Arg at position 307, was responsible for the ts phenotype of clone ts159. Substitution of sequences carrying this mutation with the corresponding sequences of the wild-type virus generated a virus that was ts for transformation. Insertion of the dominant selectable marker gene for geneticin resistance (neor) into ts159 did not disrupt mos expression or its ts phenotype. neor-ts159 facilitates the study of mos action by allowing the selection of infected cells at the nonpermissive temperature before mos transformation has been induced. Furthermore, infected cells which show no obvious phenotype alteration due to mos expression can be identified by their Neor phenotype.

Molecular cloning and physical characterization of integrated equine infectious anemia virus: molecular and immunologic evidence of its close relationship to ovine and caprine lentiviruses

Molecular clones of the integrated form of the genome of equine infectious anemia virus (EIAV), the etiologic agent of a naturally occurring, worldwide disease of horses, were obtained. The restriction map of a full-length genome was determined. Additional evidence for the close evolutionary relationship between EIAV and a prototype lentivirus (caprine arthritis encephalitis virus) was acquired by Southern blotting and immunological analyses. An interspecies radioimmunoassay was developed in which EIAV and ovine and caprine lentiviruses could be detected equally well. These studies make available precisely defined reagents to pursue the study of the mechanisms of pathogenesis of lentiviral induced diseases.

Persistent expression of v-mos oncogene in transformed cells that revert to nonmalignancy after prolonged treatment with interferon

BALB/c embryonic fibroblasts productively transformed by Moloney sarcoma virus and cultivated for over 600 generations in the presence of mouse alpha/beta interferon reverted to an apparently normal phenotype and were unable to produce tumors in nude mice. Nevertheless, the presence of an integrated Moloney sarcoma virus genome in the nonmalignant Moloney sarcoma virus-transformed interferon-treated cell DNA could be shown by focus formation upon transfection and by hybridization with a v-mos probe. After digestion with various restriction endonucleases, similar hybridization patterns of v-mos sequences were obtained with DNAs from both reverted and transformed cells. However, additional integration sites and at least twice as many copies of the oncogene were found in the nonmalignant Moloney sarcoma virus-transformed interferon-treated cell DNA. Polyadenylylated RNA extracted from reverted and control cells contained two mos-specific transcripts. Interestingly, the nonmalignant Moloney sarcoma virus-transformed interferon-treated cells produced helper virus, but no detectable mos-containing virions, suggesting that a posttranscriptional block in the v-mos gene expression had occurred in these cells. It should be stressed that, after up to 100 additional passages, cells cultured in the absence of interferon maintained their nontumorigenic character in spite of the persistent transcription of the mos oncogene.

The pathophysiology of murine retrovirus-induced leukemias

Murine leukemia viruses (MuLVs) are retroviruses which induce a broad spectrum of hematopoietic malignancies. In contrast to the acutely transforming retroviruses, MuLVs do not contain transduced cellular genes, or oncogenes. Nonetheless, MuLVs can cause leukemias quickly (4 to 6 weeks) and efficiently (up to 100% incidence) in susceptible strains of mice. The molecular basis of MuLV-induced leukemia is not clear. However, the contribution of individual viral genes to leukemogenesis can be assayed by creating novel viruses in vitro using recombinant DNA techniques. These genetically engineered viruses are tested in vivo for their ability to cause leukemia. Leukemogenic MuLVs possess genetic sequences which are not found in nonleukemogenic viruses. These sequences control the histologic type, incidence, and latency of disease induced by individual MuL Vs.

Nucleotide sequence and biochemical activities of the Moloney murine sarcoma virus strain HT-1 mos gene

The nucleotide sequence of the Moloney murine sarcoma virus strain HT-1 (HT1MSV) mos gene differs from that of the cellular mos gene in three positions, but these are silent changes, and the amino acid sequence of the v-mos and c-mos open reading frames are identical. We have overproduced the mos HT1MSV (equivalent to c-mos) in Escherichia coli under the control of phage lambda promoter (pL). The E. coli p40mos protein thus obtained was partially purified and examined for several biochemical activities. We show that the p40mos binds ATP analog p-fluorosulfonylbenzoyladenosine and exhibits ATPase activity.

Molecular cloning of integrated caprine arthritis-encephalitis virus

A full-length DNA clone of the exogenous retrovirus, caprine arthritis-encephalitis virus (CAEV), was isolated from high molecular weight DNA of CAEV-infected Himalayan tahr ovary cells. Although other restriction maps of CAEV have been published, this is the first time that the proviral DNA has been cloned. The restriction enzyme map of the clone was determined and found to be identical to that of unintegrated linear CAEV DNA except for the presence of cellular flanking sequences. These findings establish that lentiviruses are able to integrate within the infected host cellular genome. The cloned CAEV genome was shown to contain terminal repeats of approximately 450 base pairs in length, and its restriction enzyme map was oriented with respect to the direction of viral RNA transcription. When the cloned CAEV DNA was used as a molecular probe, it failed to detect related proviral sequences in the genomes of a variety of vertebrate species, including the goat, sheep, horse, mouse, and man. When CAEV DNA was hybridized under relaxed conditions to a variety of cloned DNAs, representing different oncoviral genera, homology to mouse mammary tumor virus (MMTV) was observed, while no homology to avian type C or mammalian type A, C, and D retroviruses was detected. This homology was localized to a region in MMTV corresponding to the 3' end of the gag gene and the 5' end of the pol gene.

Long terminal repeat sequences impart hematopoietic transformation properties to the myeloproliferative sarcoma virus

The myeloproliferative sarcoma virus not only transforms fibroblasts but also causes extensive expansion of the hematopoietic stem cell compartment on infection of adult mice. Similar to the Moloney sarcoma virus, it carries the mos oncogene. Moloney sarcoma virus, however, does not induce myeloproliferation and leukemia in adult mice. The difference between the two viruses was explored by using their molecularly cloned genomes and the cellular mos oncogene to construct recombinant genomes. It was shown that the U3 region of the viral long terminal repeat (LTR) has a decisive function in determining the target cell specificity of the myeloproliferative sarcoma virus. Any mos gene, whether of cellular or viral origin, is sufficient in conjunction with the proper LTR to induce myeloproliferation. Our results indicate that the pathogenicity of acutely transforming viruses is determined not only by the oncogene but also by sequences in the viral LTR.

Comparison of myeloproliferative sarcoma virus with Moloney murine sarcoma virus variants by nucleotide sequencing and heteroduplex analysis

The myeloproliferative sarcoma virus (MPSV) was derived by passage of Moloney sarcoma virus (Mo-MuSV) in adult mice. Mo-MuSV variants transform fibroblasts. However, MPSV also affects erythroid, myeloid, and hematopoietic stem cells. The MPSV proviral genome, two temperature-sensitive mutants derived from it, Mo-MuSV variant M1, and Moloney murine leukemia virus (Mo-MuLV) were compared by heteroduplex mapping. MPSV wild type was found to have 1 kilobase pair deleted from the pol gene and to contain v-mos-related sequences. The 3' end of MPSV, including the oncogene-helper junctions, the v-mos gene, and the 3' long terminal repeat, was sequenced and compared with sequences of Mo-MuLV, MSV-124, and the mouse oncogene c-mos. From these data, MPSV appears to be either closely related to the original Mo-MuSV or an independent recombinant of Mo-MuLV and c-mos. Five possible explanations of the altered specificity of MPSV are considered. (i) The MPSV mos protein has properties inherent in c-mos but lost by other Mo-MuSV mos proteins. (ii) The MPSV mos protein has altered characteristics due to amino acid changes. (iii) Due to a frameshift, MPSV codes for a mos protein truncated at the amino terminal and also a novel peptide. (iv) A second novel peptide may be encoded from the 3' env region. (v) MPSV has long terminal repeats and an enhancer sequence more like Mo-MuLV than Mo-MuSV, with a consequently altered target cell specificity.

Frequent generation of nonrescuable reorganized Moloney murine sarcoma viral genomes

Nonproducer transformants infected with wild-type Moloney murine sarcoma virus were screened for the generation of variants with reorganized genomes. Seven of 20 lines contained such viral genomes, 5 of which were found to be nonrescuable. Blotting analysis indicated that viral RNA molecules transcribed from these variant genomes could not be encapsidated into virions. The nonrescuable genomes were molecularly cloned and all were found to have suffered deletions or deletions/inversions involving the 5' long terminal repeat as well as some adjacent sequences. Nucleotide sequence analysis suggested that the long terminal repeat or the tetranucleotides G-G-T-C and G-A-C-C (or both) were involved in the generation of these mutants. Transfection studies showed that the cloned DNAs of the 5 mutants transformed NIH/3T3 monolayers. Removal of the 3' long terminal repeat from the genomes that lacked the 5' long terminal repeat or carried it in an inverted orientation abolished or considerably reduced the transforming activity.

Demonstration of virus particles in Moloney murine sarcoma virus-induced periosteal bone in mice

Balb/c mice were inoculated intramuscularly with Moloney murine sarcoma virus in one of the hind legs. This led to the rapid development of a regressive sarcoma and also to the proliferation and osteogenic differentiation of cells in the adjacent periosteum. Examination of the tissues by transmission electron microscopy revealed the presence of type A and C virus particles within the sarcoma cells as well as within the cells of the newly formed bone. Extracellular type C virus particles were formed by budding from the cell surface and by release from disintegrating cells. No virus particles were found in the bone or the surrounding soft tissues of the contralateral, noninfected leg. These observations suggest that viral infection of periosteal cells are at least partly responsible for the osteogenic response associated with the virus-induced sarcoma. Production of growth factors by the sarcoma cells could also contribute to this process.

The transforming protein of Moloney murine sarcoma virus is a soluble cytoplasmic protein

The transforming gene, v-mos, of Moloney murine sarcoma virus (M-MuSV) encodes a 37,000-dalton phosphoprotein, p37mos. Since the biochemical function of this protein is unknown, we have determined the subcellular location of p37mos in M-MuSV 124-transformed cells. Using two different methods of cell lysis and fractionation, we found that newly synthesized as well as mature p37mos is a soluble cytoplasmic protein. In agreement with these results, immunofluorescent staining of cells acutely infected with M-MuSV 124, using an antiserum directed against a synthetic v-mos peptide, produced a diffuse cytoplasmic pattern. Gel filtration experiments and glycerol gradient sedimentation analysis suggest that the bulk of p37mos exists as a monomer and is not involved in a specific association with other cellular proteins. These properties of p37mos are different from those of other characterized retroviral transforming proteins.

Detection of an 85,000-dalton phosphoprotein in ts110 murine sarcoma virus-infected cells with antiserum against a v-mos peptide

We have used an antiserum directed against a synthetic v-mos peptide (anti-C3 serum) to screen ts110 murine sarcoma virus (MuSV)-infected cells for the presence of v-mos-encoded proteins. Anti-C3 serum specifically recognized an 85,000-dalton protein doublet (P85) from [35S]methionine-labeled ts110 MuSV-infected producer cells grown at 32 degrees C, the permissive temperature for transformation. The P85 doublet was also recognized by an antiserum directed against the viral gag protein p15. P85 was present but at 2- to 10-fold-lower levels in ts110 MuSV-infected producer cells grown at 39 degrees C, the restrictive temperature for transformation. The P85gag-mos fusion product was the only v-mos protein reproducibly detected in this ts110 MuSV-transformed cell line. Immunoprecipitation of 32P-labeled cells with anti-C3 serum revealed that the upper band of the P85 doublet is phosphorylated, containing mostly phosphoserine and some phosphothreonine. Cells acutely infected with ts110 MuSV contained slightly higher levels of P85 than did the ts110 MuSV-infected producer cell line. Anti-C3 serum specifically recognized a 33,000-dalton protein (p33) in the acutely infected cells labeled with [35S]methionine. p33 was present in trace amounts and may represent a previously unidentified ts110 MuSV-encoded v-mos protein.

Naturally occurring retroviruses (RNA tumor viruses). I

This is the first of two papers describing the naturally occurring retroviruses (RNA tumor viruses). Here, the general properties of these viruses and the biology of the fish, reptilian, chicken, and mouse retroviruses are described. In the next issue of Cancer Investigation the biologic properties of the cat, cattle, primate, and newly discovered human retroviruses will be discussed.

Activation of a cellular oncogene by DNA rearrangement: possible involvement of an IS-like element

The cellular oncogene c-mos is rearranged in a mouse myeloma and the tumour mRNA contains transcripts hybridizing with a v-mos probe. The rearranged gene (rc-mos) was cloned in lambda phage and shown to transform mouse fibroblasts in transfection assays, rc-mos differs from its progenitor, c-mos, only at the 5' end of the gene, where c-mos sequences have been substituted by a novel cellular DNA fragment. This fragment contains a 159-base pair (bp) insertion sequence (IS)-like element localized immediately 5' to the junction with c-mos. This is the first demonstration in a non-virally-induced tumour of activation of a cellular oncogene by a mechanism possibly involving DNA transposition.

Rauscher murine leukemia virus: molecular cloning of infectious integrated proviral DNA

The integrated proviral genome of Rauscher murine leukemia virus was molecularly cloned in a bacteriophage Charon 4A vector after the proviral sequences were enriched by sequential RPC-5 column chromatography and sucrose gradient centrifugation. A recombinant DNA clone, lambda-RV-1, possessing a 12-kilobase-pair EcoRI insert, was shown to contain the entire 8.8-kilobase-pair leukemia virus genome flanked by rat cellular sequences at the 5' and 3' ends. This DNA fragment was biologically active, inducing the release of virion-associated reverse transcriptase activity with as little as 10 ng of DNA insert. The virus induced XC plaque formation at high titers on NIH/3T3 and BALB/3T3 cells and demonstrated identity with the parental virus in radioimmunoassays for the highly type-specific gag gene-coded p12 protein. The molecularly cloned Rauscher murine leukemia virus should be useful in studying the molecular mechanisms involved in the transformation of specific lymphoid target cells by chronic mouse leukemia viruses.

Cellular Moloney murine sarcoma (c-mos) sequences are hypermethylated and transcriptionally silent in normal and transformed rodent cells

Moloney murine sarcoma virus carries an oncogenic sequence (v-mos) which is homologous to a single copy gene (c-mos) present in the normal cells of several vertebrate species. Because of the possible significance of c-mos sequences in normal development and malignant transformation induced by physical or chemical agents, we have examined the state of integration, methylation, and transcriptional activity of c-mos sequences in a variety of normal rodent tissues, normal cell lines, or cell lines transformed by radiation or chemical carcinogens. DNA-DNA hybridization, utilizing the Southern blotting technique and a plasmid-derived DNA probe representing the v-mos sequence, gave no evidence for rearrangements of the c-mos sequence in the DNAs obtained from these diverse cell types. Parallel studies employing the restriction enzyme isoschizomers HpaII and MspI indicated that in all of these cell types the c-mos sequences were heavily methylated. In addition, analysis of cellular RNAs by blot hybridization with the v-mos probe failed to detect evidence of transcription of the c-mos sequences in any of these cell types. This was in contrast to a Moloney sarcoma virus-transformed cell line in which we found that the integrated v-mos sequence was both undermethylated and extensively transcribed. Thus, it would appear that c-mos sequences do not play a role in the transformation of rodent cells by chemical or physical agents, although the possible role of other endogenous onc sequences remains to be determined.

Molecular cloning and chromosomal mapping of a human locus related to the transforming gene of Moloney murine sarcoma virus

Human DNA was analyzed for the presence of sequences homologous to the transforming gene (v-mos) of Moloney murine sarcoma virus. A single 2.5-kilobase pair (kbp) EcoRI-generated fragment of human DNA was identified by using cloned v-mos as probe. This DNA was molecularly cloned in a bacteriophage vector. By heteroduplex and restriction enzyme analyses, this human DNA fragment, designated c-mos (human), contained a 0.65-kbp region of continuous homology with v-mos and was present as a single copy in human DNA. By testing for the presence of c-mos (human) in somatic cell hybrids possessing various numbers of human chromosomes, as well as in subclones of such hybrids, it was possible to assign c-mos (human) to human chromosome 8.

Identification of proteins encoded by the Gazdar murine sarcoma virus genome by in vitro translation and comparison with Moloney murine sarcoma virus 124

The gene products of Gazdar murine sarcoma virus (Gz-MuSV) were identified by in vitro translation of Gz-MuSV virion RNA. An overlapping set of proteins with approximate molecular weights of 37,000 (37K), 33K, 24K, and 18K were synthesized from the transforming gene of Gz-MuSV, v-mosGz. In addition, Gz-MuSV-specific RNA directed the in vitro synthesis of a 62K gag gene protein and a 37.5K env gene-related product. The Gz-MuSV-specific in vitro translation products were compared with the in vitro translation products of M-MuSV 124, an independent isolate with a similar v-mos gene. This analysis showed that the 62K Gz-MuSV gag gene protein and the 37K, 33K, 24K, and 18K v-mosGz proteins were almost identical to the M-MuSV 124 62K (gag) and 37K, 33K, 24K, and 18K (v-mosMo) proteins that we previously identified and characterized. The 37.5K env gene product from Gz-MuSV does not have a correlate in the M-MuSV 124 translation products. These results were analyzed in the context of expectations based on similarities and differences in genetic organization of these two viral genomes.

Chromosomal mapping of the simian sarcoma virus onc gene analogue in human cells

The primate cell-derived transforming gene (v-sis) of simian sarcoma virus (SSV) is represented as a single copy marker within cellular DNAs of mammalian species including human. The human analogue of v-sis can be distinguished from its rodent counterparts by Southern blotting analysis of EcoRI-restricted DNAs. By testing for the presence of the human v-sis-related fragment, c-sis (human), in somatic cell hybrids possessing varying numbers of human chromosome, as well as in segregants of such hybrids, it was possible to assign c-sis to human chromosome 22.

possible role of a retrovirus in the expression of tumor-specific antigens of the Meth A sarcoma

The serologically defined tumor-specific surface antigen (TSSA) of the chemically-induced BALB/c Meth A sarcoma, highly restricted to one of 20 sarcomas of BALB/c origin, has been detected on a Moloney murine sarcoma virus (Mo-MuSV)-transformed BALB/c 3T3 cell lines, designated IIA(v). The immunogenicity of the IIA(v) cell in tumor-rejection assays was specific for the Meth A sarcoma, supporting the evidence for a close relationship between the TSSA and the tumor-associated transplantation antigen (TATA) of this tumor. Infection of SC-I cells with retroviruses present in cultured filtrates of IIA(v) cells resulted in Meth A antigen expression. The retroviruses associated with Meth A antigen expression have been tentatively identified as replication and/or transformation-defective XC- MuLV. The possible roles of Mo-MuSV and cellular genes of the BALB/c strain of mice in the expression of the Meth A antigen are discussed.

Detection of a transforming gene product in cells transformed by Moloney murine sarcoma virus

We identified, in cells transformed by Moloney murine sarcoma virus (M-MuSV clone 124), a protein encoded by the M-MuSV transforming gene, v-mos. An antiserum against a synthetic peptide corresponding to the C terminus of a protein predicted from the v-mos nucleotide sequence specifically recognizes a protein doublet of approximately 37,000 daltons from 35S-methionine-labeled M-MuSV 124-transformed producer cells. By peptide mapping, this protein is almost identical to the 37 kd in vitro translation product from the M-MuSV v-mos gene. Immunoprecipitates from 32P-labeled cells contain a single v-mos-specific phosphoprotein, which has at least six sites of phosphorylation containing phosphoserine. Pulse-chase experiments show that the lower band in the 35S-methionine-labeled doublet is the primary translation product, which is modified, probably by phosphorylation, to yield the upper band. A similar mos protein is immunoprecipitated from HT1-MuSV-transformed cells, but not from uninfected NIH/3T3 cells. These mos proteins are present at very low levels in transformed cell lines. Cells acutely infected with M-MuSV 124, however, transiently contain much higher levels of the mos protein. These high levels coincide with extensive cell mortality.

Demonstration of biological activity and nucleotide sequence of an in vitro synthesized clone of the Moloney murine sarcoma virus mos gene

A clone of the Moloney murine sarcoma virus mos gene derived by in vitro reverse transcription was characterized. When assayed for focus formation by DNA transfection on NIH/3T3 cells, this clone was biologically inactive, presumably due to the absence of a long terminal repeat sequence. Therefore, a long terminal repeat was inserted into the clone by in vitro recombination, after which the most gene was able to transform NIH/3T3 cells efficiently. The nucleotide sequence encompassing the transforming region of this clone was determined. A single long open reading frame was observed, which potentially encodes a polypeptide of 41,000 daltons. This open reading frame initiates with the first five amino acids of the murine leukemia virus env gene, after which it enters the mos sequence, where it terminates. The nucleotide sequence described in this paper was compared with other sequences of mos in an effort to resolve discrepancies in the position of the long open reading frame. Although Moloney murine sarcoma virus retains the 3' splicing site of the murine leukemia virus env gene, a mos-specific mRNA which corresponds structurally to the murine leukemia virus env mRNA was not identified. The sequence described here revealed a single nucleotide change in the proposed env gene 3' splicing site which was retained in Moloney murine sarcoma virus. This deviation from the consensus 3' splicing sequence may underlie the observed absence of mos expression via the env gene splicing pathway.

Expression of transforming region of Moloney murine sarcoma virus in Escherichia coli as a fusion protein with small tumor antigen of polyoma virus

Bacterial expression of the transforming region of Moloney murine sarcoma virus, designated mos, was obtained as a fusion protein with a portion of the small tumor antigen of polyoma virus. This was accomplished by fusing the entire mos open reading frame, encoding a 41,000-dalton protein, with a plasmid that expresses a beta-galactosidase-polyoma fusion protein under lac operon control. The resulting plasmid directed synthesis of the predicted polyoma antigen-sarcoma virus fusion protein of 59,000 daltons. This protein was immunoprecipitated by an anti-polyoma tumor antigen antiserum that recognized polyoma determinants at the NH2 terminus of the hybrid protein. This protein was also immunoprecipitated by an antiserum directed against a synthetic peptide containing the 12 COOH-terminal amino acids encoded by the mos open reading frame. This work confirms the existence of a long open reading frame in the mos gene and resolves a discrepancy between different nucleotide sequences for its COOH-terminal coding region.

Isolation of a transformation-defective deletion mutant of Moloney murine sarcoma virus

A transformation-defective (td) deletion mutant of Moloney murine sarcoma virus (td Mo-MSV) and a transforming component termed Mo-MSV 3 were cloned from a stock of clone 3 Mo-MSV. To define the defect of the transforming function, the RNA of td Mo-MSV was compared with those of Mo-MSV 3 and of another transforming variant termed Mo-MSV 124 and with helper Moloney murine leukemia virus (Mo-MuLV). The RNA monomers of td Mo-MSV and Mo-MSV 3 comigrated on polyacrylamide gels and were estimated to be 4.8 kilobases (kb) in length. In agreement with previous analyses, the RNA of Mo-MSV 124 measured 5.5 kb and that of Mo-MuLV measured 8.5 kb. The interrelationships among the viral RNAs were studied by fingerprinting and mapping of RNase T(1)-resistant oligonucleotides (T(1)-oligonucleotides) and by identification of T(1)-oligonucleotides present in hybrids formed by a given viral RNA with cDNA's made from another virus. The nontransforming td Mo-MSV RNA lacked most of the Mo-MSV-specific sequence, i.e., the four 3'-proximal T(1)-oligonucleotides of the six T(1)-oligonucleotides that are shared by the Mo-MSV-specific sequences of Mo-MSV 3 and Mo-MSV 124. The remaining two Mo-MSV-specific oligonucleotides identified td Mo-MSV as a deletion mutant of MSV rather than a deletion mutant of Mo-MuLV. td Mo-MSV and Mo-MSV 124 exhibited similar deletions of gag, pol, and env sequences which were less extensive than those of Mo-MSV 3. Hence, td Mo-MSV is not simply a deletion mutant of Mo-MSV 3. In addition to their MSV-specific sequences, all three MSV variants, including td Mo-MSV, shared the terminal sequences probably encoding the proviral long terminal repeat, which differed from their counterpart in Mo-MuLV. This may indirectly contribute to the oncogenic potential of MSV. A comparison of td Mo-MSV sequences with either Mo-MSV 124 or Mo-MSV 3 indicated directly, in a fashion similar to the deletion analyses which defined the src gene of avian sarcoma viruses, that Mo-MuLV-unrelated sequences of Mo-MSV are necessary for transformation. A definition of transformation-specific sequences of Mo-MSV by deletion analysis confirmed and extended previous analyses which have identified Mo-MuLV-unrelated sequences in Mo-MSV RNA and other studies which have described transformation of mouse 3T3 fibroblasts upon transfection with DNAs containing the Mo-MSV-specific sequence.

Cellular genes analogous to retroviral onc genes are transcribed in human tumour cells

Polyadenylated RNAs of certain human tumour cell lines are shown to contain transcripts related to the cell-derived transforming onc genes of molecularly cloned primate, murine or avian transforming retrovirus genomes. Thus, analogues of retroviral transforming genes are both present and frequently expressed in human neoplastic cells.

Analysis of v-mos encoded proteins in cells transformed by several related murine sarcoma viruses

We have used antisera against synthetic peptides to identify and characterize a 37,000 dalton v-mos encoded protein (p37mos) in cells transformed by M-MuSV 124. p37mos, a phosphoprotein, comprises only about 0.0005% of total cellular protein in cell lines transformed by M-MuSV 124. NIH 3T3 cells acutely infected with M-MuSV 124, however, contain 30-100-fold more p37mos. These elevated levels of p37mos correlate with striking morphological changes and cell death in the acutely infected cell population. Using the antipeptide antisera, we have extended the analysis of v-mos proteins to include several other MuSV variants that contain a similar v-mos gene to M-MuSV 124. With the exception of P85, the gag-mos fusion protein from ts110 MuSV, the v-mos gene of these variants is expressed as a 35,000-37,000 dalton protein (size depending on the particular virus).

Cellular Moloney murine sarcoma (c-mos) sequences are hypermethylated and transcriptionally silent in normal and transformed rodent cells

Moloney murine sarcoma virus carries an oncogenic sequence (v-mos) which is homologous to a single copy gene (c-mos) present in the normal cells of several vertebrate species. Because of the possible significance of c-mos sequences in normal development and malignant transformation induced by physical or chemical agents, we have examined the state of integration, methylation, and transcriptional activity of c-mos sequences in a variety of normal rodent tissues, normal cell lines, or cell lines transformed by radiation or chemical carcinogens. DNA-DNA hybridization, utilizing the Southern blotting technique and a plasmid-derived DNA probe representing the v-mos sequence, gave no evidence for rearrangements of the c-mos sequence in the DNAs obtained from these diverse cell types. Parallel studies employing the restriction enzyme isoschizomers HpaII and MspI indicated that in all of these cell types the c-mos sequences were heavily methylated. In addition, analysis of cellular RNAs by blot hybridization with the v-mos probe failed to detect evidence of transcription of the c-mos sequences in any of these cell types. This was in contrast to a Moloney sarcoma virus-transformed cell line in which we found that the integrated v-mos sequence was both undermethylated and extensively transcribed. Thus, it would appear that c-mos sequences do not play a role in the transformation of rodent cells by chemical or physical agents, although the possible role of other endogenous onc sequences remains to be determined.

DNA sequences homologous to vertebrate oncogenes are conserved in Drosophila melanogaster

Sequences homologous to the oncogene sequences of acute RNA tumor viruses have been shown to be highly conserved within vertebrates. In the present work, eight different oncogene DNA sequences have been used as probes to search for homologous sequences in the DNA of organisms of other phyla. Five of these probes hybridized to the DNA of Drosophila melanogaster. Abelson leukemia virus probe detected a single homologous DNA fragment in Drosophila DNA. In contrast, probes prepared from the genomes of Harvey, avian, and feline sarcoma viruses and avian myelocytomatosis virus hybridized with multiple homologous sequences in Drosophila DNA. The identification of sequences homologous to vertebrate oncogenes in invertebrates demonstrates both a high degree of conservation of these genes and a wide distribution among divergent species. It seems likely that sequences homologous to vertebrate oncogenes play a crucial role in metazoan metabolism.

Structural organization and biological activity of molecular clones of the integrated genome of a BALB/c mouse sarcoma virus

BALB/c mouse sarcoma virus (BALB-MSV) is a spontaneously occurring transforming retrovirus of mouse origin. The integrated form of the viral genome was cloned from the DNA of a BALB-MSV-transformed nonproducer NRK cell line in the Charon 9 strain of bacteriophage lambda. In transfection assays, the 19-kilobase-pair (kbp) recombinant DNA clone transformed NIH/3T3 mouse cells with an efficiency of 3 X 10(4) focus-forming units per pmol. Such transformants possessed typical BALB-MSV morphology and released BALB-MSV after helper virus superinfection. A 6.8-kbp DNA segment within the 19-kbp DNA possessed restriction enzyme sites identical to those of the linear BALB-MSV genome. Long terminal repeats of approximately 0.6 kbp were localized at either end of the viral genome by the presence of a repeated constellation of restriction sites and by hybridization of segments containing these sites with nick-translated Moloney murine leukemia virus long terminal repeat DNA. A continuous segment of at least 0.6 and no more than 0.9 kbp of helper virus-unrelated sequences was localized toward the 3' end of the viral genome in relation to viral RNA. A probe composed of these sequences detected six EcoRI-generated DNA bands in normal mouse cell DNA as well as a smaller number of bands in rat and human DNAs. These studies demonstrate that BALB-MSV, like previously characterized avian and mammalian transforming retroviruses, arose by recombination of a type C helper virus with a well-conserved cellular gene.

Complete nucleotide sequence and organization of the Moloney murine sarcoma virus genome

The complete nucleotide sequence of a mammalian transforming retrovirus. Moloney murine sarcoma virus, has been determined. MSV, recombinant virus derived of helper viral and cellular sequences, possesses termini resembling prokaryotic transposable elements. The viral genome has the coding capacity for the Moloney murine leukemia virus gag gene product and contains large deletions in pol and env genes. A large open reading frame encompassing its cell-derived sequences codes for its putative transforming protein. The nature of some of the important domains in the viral genome has been established, and their structure is discussed in relation to their function.

Structure and functions of the Kirsten murine sarcoma virus genome: molecular cloning of biologically active Kirsten murine sarcoma virus DNA

The unintegrated closed circular form of viral DNA prepared from NIH3T3 cells infected with Kirsten murine sarcoma virus was cloned into bacterial plasmid pBR322. The closed circular DNA, which consisted of two different-sized populations, was enriched from the virus-infected cells, linearized with BamHI, and inserted into pBR322 DNA. Four different recombinant DNAs (clones 2, 4, 6, and 7) were obtained, and a physical map of each was constructed by using various restriction enzymes. Clone 4 DNA had the largest insertion, corresponding to a complete copy of the linear DNA. This suggested that this insertion contained two copies of the 0.55-kilobase pair long terminal redundant sequence. Clone 2 and clone 6 insertion DNAs had deletions of 0.2 and 0.5 kilobase pair, respectively, which mapped near the right end (3' side of viral RNA) of the linear DNA. Clone 7 DNA appeared to have a deletion of a single copy of the large terminal redundant sequence. Transfection of BALB3T3 cells with the clone 4 DNA insertion showed that this DNA had transforming activity. The efficiency of transfection with clone 4 Kirsten murine sarcoma virus DNA was enhanced eightfold by inserting EcoRI-cleaved viral DNA into the EcoRI site of pBR322. The EcoRI-inserted DNA produced foci with single-hit kinetics, suggesting that a single molecule of Kirsten murine sarcoma virus DNA can induce transformation. Results of transfections with EcoRI-inserted Kirsten murine sarcoma virus DNA cleaved with various restriction enzymes suggested that the first 3.3-kilobase pair region at the left end of the linear DNA is important for the initiation of transformation or maintenance of transformation or both.

Translational products of Moloney murine sarcoma virus RNA: identification of proteins encoded by the murine sarcoma virus src gene

In vitro translation of virion RNA of Moloney murine sarcoma virus (MSV) strain 124 yielded major products having molecular weights of 63,000 (63K), 43K, 40K, 31K, and 24K daltons. A molecularly cloned subgenomic fragment of Moloney MSV comprised of the cellular insertion (src) region was utilized in hybridization arrest translation as a means of identifying products of the MSV src gene. MSV src DNA specifically inhibited synthesis of the 43K, 40K, 31K, and 24K proteins, implying that each of these proteins was coded within the MSV src gene. The MSV src-specific nature of this family of proteins was further confirmed by partial purification of MSV src-containing RNAs from MSV non-producer cells. In vitro translation of enriched cellular RNAs yielded products with molecular weights identical to those of the 43K family of proteins synthesized from virion RNA. Nucleotide sequence analysis of the MSV transforming region has revealed a long open reading frame which includes five methionine codons (Reddy et al., Proc. Natl. Acad. Sci. U.S.A. 77:5234-5238, 1980). The molecular weights of the four largest proteins that could be synthesized within this open reading frame corresponded closely to the molecular weights of the 43K family of proteins. Partial cyanogen bromide cleavage of each of the three largest proteins resulted in an uncleaved fragment having a molecular weight equal to that of the smallest (24K) protein. These findings provide direct biochemical evidence that the 43K, 40K, 31K, and 24K proteins are related in their carboxy-terminal regions, as well as information concerning the MSV src gene coding sequences from which each protein originates:

Molecular cloning of integrated simian sarcoma virus: genome organization of infectious DNA clones

The integrated form of simian sarcoma virus (SSV) was molecularly cloned in the Charon 16A strain of bacteriophage lambda. In transfection analysis, the recombinant viral DNAs demonstrated the ability to transform cells in tissue culture at high efficiency. Such transformants possessed typical SSV morphology, expressed simian sarcoma associated virus (SSAV) gag gene products in the absence of virus release, and released SSV after superinfection with a type C helper virus. A physical map of the 5.8-kilobase-pair (kbp) recombinant viral DNA clone, deduced from restriction endonuclease analysis, revealed a 5.1-kbp SSV genome containing 0.55-kbp-long terminal repeats flanked by 0.45 and 0.25 kbp of contiguous host cell sequences. By R-loop analysis, the viral DNA molecule contained two regions of homology to SSAV, separated by a 1.0-kbp nonhomologous region. This SSV-specific sequence was shown to be uniquely represented within the normal cellular DNA of diverse mammalian species, including human. Our results demonstrate that this primate transforming retrovirus arose in nature by recombination of a type C helper virus and a host cellular gene.

Abelson murine leukemia virus: molecular cloning of infectious integrated proviral DNA

The integrated proviral genome of Abelson murine leukemia virus (A-MuLV) was cloned in lambda gtWES . lambda B bacteriophage after EcoRI endonuclease digestion and enrichment of proviral sequences by sequential RPC-5 column chromatography and agarose gel electrophoresis. Recombinant DNA clones containing a 7.8-kilobase-pair EcoRI insert were shown to have the entire integrated A-MuLV genome with both 5' and 3' ends flanked by mink cellular DNA sequences. This DNA fragment was shown to induce focus transformation upon transfection of NIH/3T3 mouse cells. Moreover, focus-forming virus could be rescued from transformed nonproducer cells upon superinfection with a type C helper virus. A polyprotein of molecular weight 120,000 (p120) containing murine leukemia virus gag gene determinants was invariably deteced by immunoprecipitation analysis of individual transformants induced by the 7.8-kilobase-pair DNA. Molecularly cloned integrated A-MuLV in its infectious form should be of use in elucidating the mechanisms involved in transformation by this virus.

Cellular transformation by subgenomic feline sarcoma virus DNA

The genome of the Snyder-Theilen strain of feline sarcoma virus (ST-FeSV) is a 4.3-kilobase-pair (kbp) RNA molecule that contains a 1.5-kbp cellular insertion (fes gene) flanked by feline leukemia virus sequences at its 5' end (1.6 kbp) and 3' end (1.2 kbp) (Sherr et al., J. Virol. 34:200-212, 1980). DNA transfection techniques have been utilized to determine the regions of the ST-FeSV genome involved in malignant transformation. I have found that the 3.7-kbp 5'-end fragment of the ST-FeSV provirus (which corresponds to the 3.4-kbp 5'-end fragment of the viral genome) is sufficient to transform NIH/3T3 fibroblasts. Enzymes that cleave the ST-FeSV provirus DNA within the feline leukemia virus gag gene sequences or within the fes gene abolished the transforming activity. Preservation of the proviral large terminal repeats was also required for transformation. Transformed NIH/3T3 cells obtained by transfection of total or subgenomic ST-FeSV DNA expressed normal levels of the ST-FeSV gene product ST P85 and of its associated protein kinase activity. Furthermore, these cells contained high levels of phosphotyrosine residues, a biochemical marker associated with cellular transformation induced by certain retroviruses including ST-FeSV. These results, taken together, strongly support the concept that only those ST-FeSV proviral sequences necessary for ST P85 expression are involved in malignant transformation.

Transformation by cloned Harvey murine sarcoma virus DNA: efficiency increased by long terminal repeat DNA

The coding sequences for the transforming (src) protein (p21) of Harvey murine sarcoma virus have been localized to a 1.3 kilobase pair segment near the 5' end of the viral genome. Ligation of the viral terminal repeat DNA to the left end of the src region DNA markedly enhanced the low transforming efficiency of the src region DNA.