In vitro translation of virion RNA from Moloney murine sarcoma virus

Novel motor gestures for phonation during inspiration enhance the acoustic complexity of birdsong

Sound generation based on a pulmonary mechanism typically occurs during the expiratory phase of respiration. Phonation during inspiration has been postulated for the calls of some amphibians and for exceptional sounds in some human languages. No direct evidence exists for phonation during inspiration in birds, but such a mechanism has been proposed to explain very long uninterrupted songs. Here, we report the first physiological evidence for inspiratory sound production in the song of the zebra finch (Taeniopygia guttata). Motor gestures of the vocal and respiratory muscles leading to the production of inspiratory phonation differ from those of silent inspirations during song as well as from those leading to phonation during expiration. Inspiratory syllables have a high fundamental frequency, which makes them acoustically distinct from all other zebra finch song syllables. Furthermore, young zebra finches copy these inspiratory syllables from their tutor song, producing them during inspiration. This suggests that physical limitations confine the production of these sounds to the inspiratory phase in zebra finches. These findings directly demonstrate how novel respiratory-vocal coordination can enhance the acoustic structure of birdsong, and thus provide insight into the evolution of song complexity.

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.

Biologically active mutants with deletions in the v-mos oncogene assayed with retroviral vectors

We have constructed retroviral expression vectors by manipulation of the Moloney murine leukemia virus genome such that an exogenous DNA sequence may be inserted and subsequently expressed when introduced into mammalian cells. A series of N-terminal deletions of the v-mos oncogene was constructed and assayed for biological activity with these retroviral expression vectors. The results of the deletion analysis demonstrate that the region of p37mos coding region upstream of the third methionine codon is dispensable with respect to transformation. However, deletion mutants of v-mos which allow initiation of translation at the fourth methionine codon have lost the biological activity of the parental v-mos gene. Furthermore, experiments were also carried out to define the C-terminal limit of the active region of p37mos by the construction of premature termination mutants by the insertion of a termination oligonucleotide. Insertion of the oligonucleotide just 69 base pairs upstream from the wild-type termination site abolished the focus-forming ability of v-mos. Thus, we have shown the N-terminal limit of the active region of p37mos to be between the third and fourth methionines, while the C-terminal limit is within the last 23 amino acids of the protein.

Lysine residue 121 in the proposed ATP-binding site of the v-mos protein is required for transformation

The transforming gene product encoded by Moloney murine sarcoma virus clone 124, p37mos, contains a lysine residue (lysine-121) that is conserved among all members of the protein kinase family. This lysine has been shown to be part of a conserved ATP-binding site in both the catalytic subunit of the cAMP-dependent protein kinase and p60v-src. We wished to determine whether this lysine is required for the transforming activity of p37mos. Two site-specific mutations were therefore constructed, which result in the substitution of an aspartic acid or arginine codon in place of the codon for lysine-121. Both mutations abolished the ability of the mos gene to transform cells. These results show that lysine-121 is required for the ability of p37mos to transform cells and provide evidence for an ATP-binding site in p37mos. Furthermore, these results suggest that the conserved lysine residue is specifically involved in the catalytic activity of protein kinases in general.

Biologically active mutants with deletions in the v-mos oncogene assayed with retroviral vectors

We have constructed retroviral expression vectors by manipulation of the Moloney murine leukemia virus genome such that an exogenous DNA sequence may be inserted and subsequently expressed when introduced into mammalian cells. A series of N-terminal deletions of the v-mos oncogene was constructed and assayed for biological activity with these retroviral expression vectors. The results of the deletion analysis demonstrate that the region of p37mos coding region upstream of the third methionine codon is dispensable with respect to transformation. However, deletion mutants of v-mos which allow initiation of translation at the fourth methionine codon have lost the biological activity of the parental v-mos gene. Furthermore, experiments were also carried out to define the C-terminal limit of the active region of p37mos by the construction of premature termination mutants by the insertion of a termination oligonucleotide. Insertion of the oligonucleotide just 69 base pairs upstream from the wild-type termination site abolished the focus-forming ability of v-mos. Thus, we have shown the N-terminal limit of the active region of p37mos to be between the third and fourth methionines, while the C-terminal limit is within the last 23 amino acids of the protein.

Use of the mouse mammary tumor virus long terminal repeat to promote steroid-inducible expression of v-mos

We used the mouse mammary tumor virus long terminal repeat to promote dexamethasone-regulated expression of the Moloney murine sarcoma virus (M-MSV) transforming gene, v-mos. A recombinant DNA vector containing the mouse mammary tumor virus long terminal repeat fused to the M-MSV 124 v-mos gene was cotransfected with a plasmid containing the herpes simplex virus thymidine kinase gene (tk) into 3T3TK- cells. Individual clones of cells which grew in hypoxanthine-aminopterin-thymidine medium were tested for dexamethasone-regulated expression of p37mos as well as several transformation-specific phenotypic parameters. In the absence of dexamethasone, the v-mos transfectants appeared morphologically similar to the control cells despite low basal levels of p37mos expression. Upon hormone treatment, the levels of p37mos increased 5- to 10-fold, coincident with morphological changes typical of M-MSV transformation of 3T3 cells. The ability to form foci in monolayers also correlated with p37mos induction. The extent of morphological changes varied in individual clones of cells with similar levels of induced p37mos. Although the induced levels of p37mos were comparable to those seen in stable M-MSV 124 virus-transformed NIH 3T3 cells, the transfectants were unable to grow in soft agar under conditions which support growth of the virus-transformed cells. Acute infection of the transfectants with M-MSV 124 virus, a situation which resulted in elevated levels of p37mos, allowed these cells to grow in soft agar. The results described in this paper suggest that different threshold levels of p37mos may be necessary for the expression of various parameters of the transformed phenotype and also that continued expression of p37mos is necessary for maintenance of the transformed state. However, it also appears that the sensitivity to given levels of p37mos varies among clonal cell lines.

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.

Transmission of the polyoma virus middle T gene as the oncogene of a murine retrovirus

Polyoma virus is a papovavirus that productively infects mouse cells. In cells of other species, such as rat cells, polyoma virus is virtually unable to replicate, and a small proportion of infected cells become stably transformed. The ability of polyoma virus to transform infected cells is determined by genes that encode the large, middle and small T antigens and which are found in the early region of the virus genome. We have inserted the transforming region of polyoma virus into a murine leukaemia virus (MLV) vector, to generate a replication-defective transforming retrovirus which for the first time allows efficient transformation of mouse cells by the polyoma virus middle T gene. During the life cycle of this recombinant virus the intervening sequence present in the original polyoma virus middle T gene was removed. The recombinant virus that we have constructed is analogous to other acutely transforming retroviruses, and demonstrates that the polyoma middle T gene is a dominant transforming oncogene.

Coronavirus multiplication: locations of genes for virion proteins on the avian infectious bronchitis virus genome

Six overlapping viral RNAs are synthesized in cells infected with the avian coronavirus infectious bronchitis virus (IBV). These RNAs contain a 3'-coterminal nested sequence set and were assumed to be viral mRNAs. The seven major IBV virion proteins are all produced by processing of three polypeptides of ca. 23, 51, and 115 kilodaltons. These are the core polypeptides of the small membrane proteins, the nucleocapsid protein, and the 155-kilodalton precursor to the large membrane proteins GP90 and GP84, respectively. To determine which mRNAs specify these polypeptides, we isolated RNA from infected cells and translated it in a messenger-dependent rabbit reticulocyte lysate. Proteins of 23, 51, and 110 kilodaltons were produced. Two-dimensional tryptic peptide mapping demonstrated that these proteins were closely related to the major virion proteins. Fractionation of the RNA before cell-free translation permitted the correlation of messenger activities for synthesis of the proteins with the presence of specific mRNAs. We found that the smallest RNA, RNA A, directs the synthesis of P51, the nucleocapsid protein. RNA C, which contains the sequences of RNA A, directs the synthesis of the small membrane protein P23. RNA E directs the synthesis of the large virion glycoproteins. These results supported a model in which only the unique 5'-terminal domain of each IBV mRNA is active in translation and enabled us to localize genes for virion proteins on the IBV genome.

Construction and characterization of Moloney murine leukemia virus mutants unable to synthesize glycosylated gag polyprotein

Murine leukemia virus (MuLV) encodes two independent pathways for expression of the gag gene. One pathway results in processing and cleavage of the precursor Pr65gag to yield the internal capsid proteins of the virion and is analogous to gag polyprotein precursors for all classes of retroviruses. The other pathway, which is not encoded by several other classes of retroviruses, begins with a glycosylated polyprotein gPr80gag . gPr80gag is synthesized independently of Pr65gag; it contains Pr65gag peptides and additional amino-terminal protein. It is modified by further addition of carbohydrate, exported to the cell surface, and released from the cell but does not appear in virus particles. To investigate the role of glycosylated gag in MuLV infection, two mutants of Moloney MuLV (M-MuLV) deficient for synthesis of gPr80gag but able to synthesize Pr65gag were constructed. The mutants were obtained by substitution into a molecular clone of M-MuLV DNA by DNA from two acutely transforming viruses, Ableson MuLV (Ab-MuLV) and Moloney murine sarcoma virus (M-MSV). Both Ab-MuLV and M-MSV are derived from M-MuLV and they express M-MuLV gag sequences, but some strains do not synthesize glycosylated gag protein. For Ab-MuLV, a 177-base-pair Pst I fragment from the P90 strain containing the initiation codon for Pr65gag was substituted for the equivalent fragment in M-MuLV DNA. For M-MSV, 1.5 kilobases at the 5' end of the genome was substituted. Transfection of the recombined DNAs onto NIH-3T3 cells produced infectious M-MuLV, although the infected cells did not produce gPr80gag. Therefore glycosylated gag is not absolutely required for MuLV replication. Deletion of the glycosylated gag pathway did not significantly reduce the level of virus production, although a minor difference in XC plaque morphology was observed.

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.

Gag-mos Polyproteins encoded by variants of the Moloney strain of mouse sarcoma virus

Two revertants of ts110 Moloney murine sarcoma virus (MuSV) with wild-type MuSV phenotype were examined for the presence of mos gene products, ts110 MuSV has a temperature-sensitive defect in a function required to maintain the transformed phenotype. The nonproducer 6m2 cell clone transformed by ts110 produces an 85,000-Da gag-mos protein (P85gag-mos) and a 58,000-Da gag protein (P58gag). A spontaneous revertant (clone 54-5A4) of the 6m2 cell clone produces a 100,000-Da protein (P100) recognized by antisera raised against murine leukemia virus p15, p12, and p30 but lacks determinants of p10, reverse transcriptase, and gp70. P100 was specifically recognized by antisera (anti-C3) prepared against a synthetic peptide representing the predicted C-terminal 12 amino acids of Moloney MuSV v-mos gene. Normal sera or anti-C3 blocked with excess synthetic peptide did not recognize P100. Thus, P100 is a product of the gag and mos genes. P100 was found to be phosphorylated. A second wild-type revertant (clone 204-3) was obtained by superinfection of ts110 nonproducer cells with Simian sarcoma associated virus (SSAV); it was also found to contain a phosphorylated P100gag-mos protein. The 204-3 cell clone also contained two gag polyproteins (Pr60gag and Pr55gag) of the size and antigenic properties of those found in SSAV-infected cells. These results provide two examples of P100 gag-mos proteins both derived from the P85gag-mos producing 6m2 cell clone. The P100 gag-mos polyproteins are made in amounts that are easily detected by radiolabeling experiments using [3H]leucine. The intracellular viral RNAs present in 6m2 cells and the two revertant clones were also examined. All three cell clones contained a 4.0 kb RNA hybridizing to v-mos sequences but only the 6m2 clone contained a 3.5 kb mos-containing RNA. Our findings indicate that the 3.5 kb RNA codes for P85gag-mos in cell-free translation experiments (Junghans et al., 1982, J. Mol. Biol. 161, 229). These findings as they relate to the mechanism that produces P100gag-mos instead of P85gag-mos are discussed.

P85: a gag-mos polyprotein encoded by ts110 Moloney murine sarcoma virus

Antibody to a synthetic peptide (anti-C3 serum) with the predicted sequence of the C terminus of the Moloney murine sarcoma virus (strain 124) v-mos gene was used in immunoprecipitation experiments with cytoplasmic extracts of a clone of NRK cells infected with ts110 Moloney murine sarcoma virus, termed 6m2 cells. ts110 Moloney murine sarcoma virus codes for two viral proteins of 85,000 and 58,000 M(r), termed P85 and P58, respectively, in nonproducer 6m2 cells maintained at 33 degrees C. Anti-C3 serum specifically recognized [(3)H]leucine-labeled P85, but not P58, from infected cells maintained at 33 degrees C, whereas antiserum prepared against murine leukemia virus p12 recognized both proteins. Normal serum and anti-C3 serum pretreated with excess C3 peptide did not precipitate P85. Immunoprecipitation experiments after metabolic labeling of 6m2 cells with (32)P(i) showed that P85 is phosphorylated. Both anti-C3 and anti-p12 sera specifically detected (32)P-labeled P85. Cell-free translation of ts110 murine sarcoma virus/murine lukemia virus RNA produces P85, P58, and helper virus protein Pr63(gag). Anti-C3 serum specifically precipitated P85 but neither P58 nor Pr63(gag). We conclude from these studies that P85 is a product of both the gag and mos genes of ts110 murine sarcoma virus, and, therefore, it is referred to as P85(gag-mos). We have not detected any other v-mos gene product in ts110-infected cells.

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.

Recombinational junctions of variants of Moloney murine sarcoma virus: generation and divergence of a mammalian transforming gene

Different variants of Moloney murine sarcoma virus (MSV) were examined by nucleotide sequencing to compare the junctions between the acquired cellular sequence, v-mos, and the adjacent virus-derived sequences. These variants included 124-MSV, m1-MSV, and HT1-MSV and also the purportedly independent isolate Gazdar MSV. These four strains have an identical 5' junction between the murine leukemia virus env gene and the v-mos gene. This junction lies within the sixth codon of the chimeric env-mos coding region that encodes the transforming gene product. In contrast, at the 3' junction between the v-mos gene and the murine leukemia virus env gene, the three variants examined here were all different. A small deletion was found in the COOH-terminal portion of the m1-MSV env-mos coding region, indicating that the COOH terminus of this transforming gene product must be different from that of 124-MSV or HT1-MSV. The data presented here are consistent with the thesis that a virus closely related to HT1-MSV was the primordial Moloney MSV, and that all other related strains evolved from it by deletion or rearrangement. The variability observed in the Moloney MSV family is discussed in terms of possible mechanisms for the initial capture of mos sequences by the parental retrovirus and also in comparison with other transforming retrovirus families, such as Abelson murine leukemia virus and Rous sarcoma virus.

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.

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.

A generalized method of subcloning DNA fragments by restriction site reconstruction: application to sequencing the amino-terminal coding region of the transforming gene of Gazdar murine sarcoma virus

The technique of restriction site reconstruction was generalized so as to allow the subcloning of any DNA fragment and its subsequent reexcision with EcoRI, XbaI, XhoI or HindIII. After excision, the 3' terminus of each strand will be derived from the starting nucleic acid, permitting the use of such fragments as primers for nucleotide sequencing by primer extension methods. The technique was used to subclone a 56 base pair BstNI-DdeI fragment of Moloney murine sarcoma virus (Mo-MSV) as a unique HindIII-HindIII fragment. This fragment then served as a primer to sequence a portion of the RNA genome of Gazdar murine sarcoma virus (Gz-MSV). The nucleotide sequence which was obtained indicated that the transforming gene of Gz-MSV arose by at least two recombination events involving murine leukemia virus (MLV) and the cellular homologue c-mos. This analysis suggests that a virus indistinguishable from Mo-MSV was an intermediate in the formation of Gz-MSV.

Structural analysis of virion proteins of the avian coronavirus infectious bronchitis virus

We have found six major polypeptides in virions of the avian coronavirus infectious bronchitis virus grown in tissue culture: four glycoproteins, GP84, GP36, GP31, and GP28, and two non-glycosylated proteins, P51 and P23. In addition, we detected three minor species: two glycoproteins, GP90 and GP59, and one non-glycosylated protein, P14. Two-dimensional tryptic peptide mapping showed that GP36, GP31, GP28, and P23 comprise a group of closely related proteins which we have designated the "P23 family," but that the other proteins are distinct. Analysis by partial proteolytic digestion of P23 family, but that the other proteins are distinct. Analysis by partial proteolytic digestion of the P23 family labeled biosynthetically with [35S] methionine, and P23, labeled with [35S] formyl-methionine by in vitro translation of RNA from infected cells, revealed that the proteins of the P23 family differ in their amino-terminal domains. Similar analysis of GP31 and Gp36 labeled with [3H] mannose showed that the partial proteolytic fragments unique to these proteins were glycosylated. This suggests that differences in glycosylation in the amino-terminal domains contributes to the marked polymorphism os the P23 family. The results are discussed with respect to possible models for synthesis of the virion proteins.

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.

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).

Purified low-molecular-weight protein kinase from murine sarcoma virus particles catalyzes tyrosine phosphorylation endogenously but phosphorylates cellular proteins at serine

The low-molecular-weight (LMW) protein kinase associated with high-titer murine sarcoma virions have been extensively purified by ammonium sulfate fractionation. Bio-Gel P-100 gel filtration, DEAE-cellulose and carboxymethyl cellulose chromatography. The purified enzyme migrates as a 16K polypeptide in polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The enzyme catalyzes phosphotransfer with ATP as a phosphate donor to various exogenously added proteins as acceptors; it requires Mg2+ and is independent of cyclic AMP. The enzyme preparation catalyzes a low level of phosphorylation in the absence of any exogenously added substrate and forms phosphotyrosine. However, in the presence of acceptor protein molecules including total soluble cytoplasmic proteins of murine sarcoma virus-transformed mouse cells, the phosphorylated end products contain predominantly phosphoserine. The virion-associated enzyme also shows a preference for phosphorylating certain polypeptides in the soluble cytoplasmic extracts of murine sarcoma virus-transformed cells.

Purification and translation of murine mammary tumor virus mRNA's

We have studied the functions of the intracellular RNAs of mouse mammary tumor virus (MMTV) by purification and translation in vitro. Two major size classes of MMTV RNA, 35S and 24S RNA, were isolated from MMTV-infected rat (XC) cells and cultured mammary tumor cells by preparative hybridization of whole cell or polyadenylated RNA to cloned MMTV DNA covalently bound to chemically activated paper disks (diazobenzyloxymethyl paper). Genomic-length (35S) RNA was prepared free of 24S RNA by rate zonal sedimentation in sucrose gradients. Experiments using [3H]uridine-labeled cellular RNA indicated that the preparative annealing method was highly specific and capable of effecting a 300-fold enrichment for viral RNA; the recovered RNA appeared to be intact under denaturing conditions and directed synthesis of full-length gag and env polypeptides in vitro. The products of in vitro translation were identified by gel mobility, immunoprecipitation tests with antisera against gag and env products, and partial digestion with Staphylococcus V8 protease. The 35S RNA species directed synthesis of several gag-related polypeptides, including three previously reported in extracts of infected cells; 24S RNA directed synthesis of two polypeptides closely related to env proteins from infected cells. Therefore, 35S RNA includes mRNA's for gag and gag-pol, whereas 24S RNA is the mRNA for env. These results help establish the position of env on the physical map of the MMTV genome and bear upon the coding potential of the genome.

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:

Nucleotide sequence and formation of the transforming gene of a mouse sarcoma virus

The complete nucleotide sequence of the transforming gene of a mouse sarcoma virus has been determined. It codes for a protein of 374 amino acids. The nucleotide sequence of the junctions between a murine leukaemia virus and cellular sequences leading to the formation of the viral transforming gene have also been elucidated. The viral transforming sequence and its cellular homologue share an uninterrupted stretch of 1,159 nucleotides, with few base substitutions. The predicted amino acid sequence of the mouse sarcoma virus transforming gene was found to share considerable homology with the proposed amino acid sequence of the avian sarcoma virus oncogene (src) product.

Protein-coding potential of mouse mammary tumor virus genome RNA as examined by in vitro translation

The protein-coding capacity of the mouse mammary tumor virus genome has been examined by in vitro translation of genome length and polyadenylated subgenomic fragments of viral RNA. Intact genome RNA of about 35S programmed synthesis of the Pr77gag, Pr110gag and Pr160gag/pol precursors seen in infected cells in vivo. Polyadenylated RNA fragments of 18 to 28S encoded products whose tryptic peptide maps resembled those of the nonglycosylated precursor to the envelope glycoproteins, confirming the gene order 5'-gag-pol-env-3'. Translation of polyadenylated RNA fragments smaller than 18S yielded a series of related proteins whose peptide maps bore no resemblance to any of the virion structural proteins. Thus, a region of the mouse mammary tumor virus genome distal to the env gene appears to have an open reading frame sufficient to encode at least 36,000 daltons of protein as of yet unknown function.

Identification and molecular cloning of Moloney mouse sarcoma virus-specific sequences from uninfected mouse cells

When uninfected mouse cell DNA is cleaved with restriction endonuclease EcoRI, a DNA fragment of 14.0 kilobases can be identified by hybridization to cloned DNA containing sarcoma specific sequences of Moloney mouse sarcoma virus (M-MSVsrc). The cellular DNA fragment contains the entire M-MSVsrc specific sequences. The 14.0-kilobase EcoRI DNA fragment was cloned in bacteriophage lambda. The sequence organization of a recombinant clone, lambda . MTX-1, was analyzed by restriction endonuclease mapping, nuclease S1 mapping, and electron microscopy. The results indicate that lambda . MTX-1 contains an uninterrupted stretch of 1.0 kilobase similar to that found in the M-MSV genome.