Detection of oncornavirus-like particles in HeLa cells. I. Fine structure and comparative morphological classification

Evolution of primate oncornaviruses: An endogenous virus from langurs (Presbytis spp.) with related virogene sequences in other Old World monkeys

Gene sequences related to a retrovirus (oncornavirus type D) isolated from a lung cell culture from spectacled langur (Presbytis obscurus) are found in multiple copies (20-40 per haploid genome) in langur cellular DNA; partially homologous virogene sequences are present in the DNA of related Old World monkey species. Primates thus contain gene sequences for at least two distinct classes of genetically transmitted oncornaviruses, the type C class (isolated from baboons) and the type D class described here. The langur virus is partially related to Mason-Pfizer monkey virus, a type D retrovirus isolated from rhesus monkeys. Nucleic acid hybridization studies suggest that Mason-Pfizer monkey virus, now infectious among primates, was derived from an endogenous virus of langurs or from another member of the primate sub-family Colobinae.

A novel fish herpesvirus of Osmerus eperlanus

A herpesvirus of smelt (Osmerus eperlanus) was identified by thin section electron microscopy. Degenerated cells of skin lesions located on the back fin of smelt showed either intranucleic- or cytoplasmic herpesvirus-specific structures. In the nuclei "naked" virus capsids with a diameter of about 100 nm were observed. The diameter of the complete virion including its unilaterally extended envelope ranged from 200 to 350 nm. Remarkably, in complete virions the electron-opaque tegument is completely filling the region between nucleocapsid and envelope and as another unique feature the virion shows a "comet-shape" due to a long unilateral extension of its envelope. This kind of shape had been not reported for any of herpesviruses known so far. Consequently this virus was termed herpesvirus of Osmerus eperlanus (HVOE1) or Comet herpesvirus of smelt. Due to the long time storage at the nonstandard temperature of smelt virus the biological and genomic analysis of the HVOE1 was hampered. All attempts to study host range of HVOE1 failed as no virus replication was observed, indicating that infectivity was lost or the suitable cell culture was missing. The genomic DNA of HVOE1 was analyzed by DNA restriction endonucleases.

Unintended spread of a biosafety level 2 recombinant retrovirus

Background

Contamination of vertebrate cell lines with animal retroviruses has been documented repeatedly before. Although such viral contaminants can be easily identified with high sensitivity by PCR, it is impossible to screen for all potential contaminants. Therefore, we explored two novel methods to identify viral contaminations in cell lines without prior knowledge of the kind of contaminant.

Results

The first hint for the presence of contaminating retroviruses in one of our cell lines was obtained by electron microscopy of exosome-like vesicles released from the supernatants of transfected 293T cells. Random amplification of particle associated RNAs (PAN-PCR) from supernatant of contaminated 293T cells and sequencing of the amplicons revealed several nucleotide sequences showing highest similarity to either murine leukemia virus (MuLV) or squirrel monkey retrovirus (SMRV). Subsequent mass spectrometry analysis confirmed our findings, since we could identify several peptide sequences originating from monkey and murine retroviral proteins. Quantitative PCRs were established for both viruses to test currently cultured cell lines as well as liquid nitrogen frozen cell stocks. Gene fragments for both viruses could be detected in a broad range of permissive cell lines from multiple species. Furthermore, experimental infections of cells negative for these viruses showed that both viruses replicate rapidly to high loads. We decided to further analyze the genomic sequence of the MuLV-like contaminant virus. Surprisingly it was neither identical to MuLV nor to the novel xenotropic MuLV related retrovirus (XMRV) but showed 99% identity to a synthetic retrovirus which was engineered in the 1980s.

Conclusion

The high degree of nucleotide identity suggests unintended spread of a biosafety level 2 recombinant virus, which could also affect the risk assessment of gene-modified organisms released from contaminated cell cultures. The study further indicates that both mass spectrometry and PAN-PCR are powerful methods to identify viral contaminations in cell lines without prior knowledge of the kind of contaminant. Both methods might be useful tools for testing cell lines before using them for critical purposes.

Novel endogenous type D retroviral particles expressed at high levels in a SCID mouse thymic lymphoma

A xenograft model of the human disease Langerhans cell histiocytosis (LCH) was investigated with severe combined immunodeficiency (SCID) mice. Transplantation of human LCH biopsy material into SCID mice resulted in the generation of mouse tumors resembling lymphomas. A thymoma cell line (ThyE1M6) was generated from one of these mice and found to display significant levels of Mg2+-dependent reverse transcriptase activity. Electron microscopy revealed particles with type D retroviral morphology budding from ThyE1M6 cells at a high frequency, whereas control cultures were negative. Reverse transcription-PCR of virion RNA with degenerate primers for conserved regions of various mouse, human, and primate retroviruses amplified novel sequences related to primate type D retroviruses, murine intracisternal A particles, Jaagsiekte sheep retrovirus, and murine long interspersed nuclear elements but not other retroviral classes. We demonstrate that these sequences represent a novel group of endogenous retroviruses expressed at low levels in mice but expressed at high levels in the ThyE1M6 cell line. Furthermore, we propose that the activation of endogenous retroviral elements may be associated with a high incidence of thymomas in SCID mice.

Markers of type D retroviruses in children with Burkitt's-type lymphoma

Antibodies to gag-coded proteins of type D retroviruses have been detected in children with lymphadenopathy [1]. We tested 41 HIV noninfected children with lymphoproliferative diseases (27 cases of Burkitt's-type lymphoma, six cases of Hodgkin's disease, four cases of T-cell lymphoma, three cases of lymphoblastic lymphoma and one case of large-cell anaplastic lymphoma) for the presence of type D retroviral serological and genetical markers. Twenty-five healthy donors were tested as a control. DNA samples from peripheral blood lymphocytes were analyzed by the polymerase chain reaction (PCR) and Southern blotting for the presence of type D retroviral related sequences. MPMV pro-pol specific sequences have been detected in 18 out of 27 children with Burkitt's-type lymphoma. By means of Western blotting, six patients positive in PCR/Southern blotting analysis were also found to contain Mason-Pfizer monkey virus (MPMV) specific antibodies, in their sera. All children with other lymphoproliferative diseases as well as healthy donors were negative in PCR/Southern blotting and Western blotting analysis. These data suggest the possible association of type D retroviral markers with Burkitt's-type lymphoma of children.

Endogenous retroviruses in the human genome--a point of view

The search for retroviruses in human cancer cells has advanced with the discoveries of the retroviral reverse transcriptase, DNA hybridization and sequencing techniques, and polymerase chain reaction (PCR) technology. Each technological advancement has led to a better refinement and a better understanding of latent endogenous retroviruses in the human genome. With the recent developments in the Human Genome Project it is to be expected that additional information will be obtained on the role and function of these human retroviruses, their ancestral origin and, if possible, their involvement as a source for emerging new retroviruses.

Electron microscopy of the nucleocapsid from disrupted Moloney murine leukemia virus and of associated type VI collagen-like filaments

To analyze the constituents of retroviruses, the Moloney murine leukemia virus was disrupted and observed by dark-field electron microscopy. Virus disruption was achieved by several methods: osmotic shock, freezing-thawing cycles, and exposure to urea up to 4 M, to NaCl up to 1 M, and to Triton X-100. Several components associated with broken Moloney murine leukemia virus were repeatedly found in preparations. These components have been described as rings, thick filaments, chain-like filaments, threads covered with proteins, threads with buckles, and naked threads. A quantitative analysis of the occurrence of these components has been carried out. Among them, the thick filaments composed of a compact helical arrangement of small beads 5 nm in diameter were considered to represent the nucleocapsid. The protease-sensitive buckles found on some threads could be a compact form of the viral RNA associated to the nucleocapsid protein NCp10. The RNase-sensitive naked threads are interpreted as the deproteinized viral RNA itself. The ubiquitous chain-like filaments possess a periodic structure identical to that of polymerized type VI collagen. It is proposed that this adhesive protein is associated with the viral envelope taken from the cell membrane during the budding process of retroviruses.

Identification of human type D retrovirus as a contaminant in a neuroblastoma cell line

In this report we describe a type D virus isolated from a human neuroblastoma cell line (Paju). The viral RNA was isolated, partially molecularly cloned and sequenced. Our clones were shown to be identical to a human D-type retrovirus previously isolated from a human lymphoblastoid cell line. However, we obtained no evidence for the virus in earlier passage of the Paju cell line and therefore we must consider this isolate a laboratory contamination. contamination.

Insertion of SMRV-H viral DNA at the c-myc gene locus of a BL cell line and presence in established cell lines

Mutation of the c-myc gene locus has occurred during in vitro culture of the Burkitt lymphoma cell line Namalwa. Gene cloning and sequencing of this c-myc gene locus has revealed the insertion of incomplete copies of the Squirrel Monkey Retrovirus-Human (SMRV-H) proviral genome. Insertions of the SMRV-H genome were seen in all Namalwa cell lines tested, with multiple insertions being seen in some sublines. Viral particles with the morphology of type-D retrovirus, budding from these cells, were seen by transmission EM. New insertions of the genome were produced spontaneously in these cells. The origins of the type-D retrovirus and its implications for workers in the field are discussed.

Isolation of a type D retrovirus from B-cell lymphomas of a patient with AIDS

An atypical syncytial variant of a high-grade Burkitt's-type B-cell lymphoma from a patient with AIDS who was seropositive for human immunodeficiency virus type 1 was studied. A productive type D retrovirus infection was identified in early-passage cell lines derived from two lymphomas from this patient. Nucleotide and amino acid sequence analysis as well as immunologic reactivity indicated that the isolated virus was highly related to Mason-Pfizer monkey virus (MPMV). MPMV is an immunosuppressive type D retrovirus that causes an AIDS-like syndrome in rhesus macaques. Amplification of DNA from the patient's diagnostic bone marrow biopsy specimen by polymerase chain reaction generated the appropriate MPMV-specific fragments and indicated that the patient was infected with the MPMV-like retrovirus. In addition, the patient's serum contained antibodies which recognized type D viral env proteins (gp70 and gp20) and gag proteins (p27 and p14). Although there have been reports of human cell lines infected with type D retroviruses and of type D-reactive human sera, this is the first evidence of a type D retrovirus infection in a human confirmed by virus isolation, serum reactivity, and viral DNA identification in tumor tissue.

Molecular cloning of a type D retrovirus from human cells (PMFV) and its homology to simian acquired immunodeficiency type D retroviruses

Unintegrated circular proviral DNA of a type D retrovirus (PMFV) isolated from a permanent human cell line was molecularly cloned in the bacteriophage vector L47.1 and subcloned in the plasmid vector pGEM-2. A restriction endonuclease map of PMFV DNA was established using 10 different enzymes for single and multiple digestions of closed circular and cloned DNA molecules. By restriction endonuclease analysis cloned PMFV DNA represented full-length viral DNA with one long terminal repeat (LTR). The comparison of the physical map of cloned PMFV to those of other cloned type D retroviruses revealed closest homology to the map of retrovirus D/New England (pD398) and SAIDS retrovirus type 1 (SRV-1). The relatedness of PMFV to further type D retroviruses (Mason-Pfizer monkey virus, MPMV; SAIDS retrovirus type 2, SRV-2) was also demonstrated by cross-hybridization of cloned DNAs under different stringencies (i) using full-length genomic probes of PMFV, MPMV, and SRV-2 and (ii) by DNA sequence analysis of regions of the group specific antigen (gag) protease (prt), polymerase (pol), and envelope (env) genes.

Type A oncornavirus-like particles in turkey bone marrow cells transformed by avian leukemia virus

Type A oncornavirus-like particles (TAOLP) were found in the cytoplasm of turkey bone marrow cells transformed by strain Mc-31 avian leukemia virus. They resembled morphologically the cores of budding virions and the cores of immature extracellular Mc-31 virus particles. TAOLP were observed more often in T3Mc31 cells where cytopathological changes existed. TAOLP were not found in the materials from in vivo experiments. A relationship is likely to exist between TAOLP and Mc-31 virus and TAOLP could represent a side product of Mc-31 virus replication.

Biochemical and immunological characterization of structural proteins from retrovirus-D/New England and comparison to Mason-Pfizer monkey virus and permanent human fibroblast virus

Biochemical and immunological properties of retrovirus-D/New England (here referred as R-D/NE) recently isolated at the New England Regional Primate Research Center, Southborough, Ma, from a rhesus monkey with acquired immune deficiency syndrome were investigated and compared to the prototype type D retroviruses Mason-Pfizer monkey virus (MPMV) and permanent human fibroblast virus (PMFV) isolated from a breast carcinoma of a rhesus monkey and a continuous human cell line, respectively. The polypeptide composition of R-D/NE propagated in a human lymphoid B cell line (Raji cells) has been investigated using SDS-polyacrylamide gel electrophoresis. Staining with Coomassie blue and labelling with 14C amino acids revealed seven viral polypeptides with molecular weights of 4,000, 10,000, 12,000, 15,000, 18,000, 27,000, and 80,000 Da which were also shared by MPMV and PMFV. The 80,000 Da protein was shown to be a glycoprotein by incorporation of 3H glucosamine. The 18,000 Da protein was identified as a phosphoprotein of R-D/NE. p18 structural proteins of MPMV and PMFV represent phosphoproteins of their respective viruses as well. All three phosphorylated proteins contain O-phosphoserine as major phosphoamino acid. The comparison of tryptic peptide maps of the major internal structural proteins of R-D/NE, MPMV, and PMFV revealed a striking similarity among p 10/p 12 and p 15. proteins. A minor difference was detected among the tryptic peptide digests of p 4 and p 27 proteins. Antiserum against p 15 of MPMV showed a significantly weaker binding to R-D/NE than to MPMV and PMFV at high dilutions.

Isolation and characterization of covalently closed circular proviral DNA molecules of several type D retroviruses isolated from human cell lines

Infection of a human lymphoblastoid B cell line (Raji cells) with type D retroviruses, originally isolated either from subhuman primates (MPMV, LV) or from permanent human cell lines (PMFV, HeLaV, HEp-2V) led to the production of type D retrovirus particles. Subsequent cocultivation of uninfected and virus-producing Raji cells was employed for the generation of sufficient amounts of covalently closed circular DNA molecules (cccDNA). Highest amounts of cccDNA were obtained after cocultivation of virus-producing Raji cells and homologous uninfected cells at a ratio of 1 to 3 for 72 hr. The cccDNAs of type D retroviruses migrated at about 4.3 kbp compared to lambda DNA/HindIII markers. Digestion of cccDNAs with restriction endonucleases which have one recognition site generated molecules of approximately 8 kbp. The restriction endonuclease site analysis of the cccDNA of type D retroviruses revealed a genomic heterogeneity among the different isolates.

Further evidence from tryptic peptide analysis for heterogeneity among type D retroviruses

Tryptic peptide analyses were performed on the major internal structural proteins of type D retroviruses isolated originally from subhuman primate species (MPMV, SMRV, LV) and from permanent human cell lines (HeLaV, HEp-2V, PMFV). The p25 peptide maps of MPMV, LV, PMFV and HEp-2V were very similar but showed a striking dissimilarity to the p25 map of HeLaV and the p35 map of SMRV. All type D viruses included in this study could be distinguished by peptide maps of at least two of their three low-molecular-weight proteins p10, p12 and p15. These studies further demonstrate the heterogeneity among type D retroviruses.

Type D retroviruses from human cells do not contain a minor glycoprotein shared by old world monkey type D viruses

The protein patterns of type D retroviruses isolated either from permanent human cells (HeLa virus, HeLa V, and HEp-2 virus, HEp-2V) or from spectacled langur (langur virus, LV), an Old World monkey, were investigated using sodium dodecyl sulfate polyacrylamide gel electrophoresis. Labeling with 14C-amino acids and 3H-glucosamine revealed for each of these isolates five polypeptides with molecular weights of 10,000, 12,000, 15,000, 25,000 and about 68,000 and identified the 68,000 D-protein as a glycoprotein. An additional glycoprotein with a molecular weight of 20,000 (gp20) was resolved in LV similarly as in previous studies with Mason-Pfizer monkey virus. However, in accordance with our recent analysis of a third type D isolate from human cells (PMFV), gp20 was not detectable in both HeLaV and HEp-2V regardless of the cell line in which they were grown. Thus, it appears that the type D virus isolates from human cells are slightly distinct from the presently known type D retroviruses of Old World monkeys. The relevance of this finding to the origin of the human isolates, however, remains to be shown.

Ultrastructural studies on Maedi-Visna virus

Ultrastructural studies of Maedi-Visna virus (MVV) particles isolated from tissue culture fluids of MVV-infected cells as well as cultured cells infected with MVV were performed. MVV particles aree bounded by an envelope with projections loosely attached to its surface. Virions contain a core (sometimes two or more) of conical or ovoid shape enclosing an electron-dense nucleoid which is much smaller in diameter than the core and which can only be seen in ultrathin sections. A distinct core shell is to be found in most of the ultrasectioned particles. Cores, liberated from the virions by detergent treatment, exhibited the same shape as their enveloped counterparts. Budding structures with crescents underlying the cell membrane without an intermediate space seem to be bordered on their cell side by an electron-dense thin layer. Particles obviously representing intervenig stages of viral maturation showing parts of the crescents at the viral membrane and empty core shells could be found in single cases.

Purification and characterization of the RNA-directed DNA polymerase of a primate type-D retrovirus: Mason-Pfizer virus

The RNA-directed DNA polymerase of the primate type-D retrovirus Mason-Pfizer virus was purified using ion-exchange and affinity chromatography, and molecular sieving. The enzyme was shown to have a molecular weight of approx. 80 000 as determined by sedimentation analysis, molecular sieving and sodium dodecyl sulfate polyacrylamide gel electrophoresis. The purified RNA-directed DNA polymerase retained its ability to use a heteropolymeric RNA as a template. The Mason-Pfizer virus RNA-directed DNA polymerase was also characterized as to its divalent cation preference for several synthetic primertemplates and for heteropolymeric RNA. Mg2+ was preferred as its divalent cation for all primer-templates except oligo(dG).poly(rC)m for which it prefers Mn2+. The Mason-Pfizer virus enzyme was also shown to have a pH optimum of 8-8.5 and a temperature optimum of 37-40 degrees C. The stability of the Mason-Pfizer virus RNA-directed DNA polymerase was shown to differ when measured using different primer-templates.

Evidence for type-C retrovirus production by Burkitt's lymphoma-derived cell line

Burkitt's lymphoma cell line, P3HR-I, was found to secrete virions with properties of known type-C RNA tumor viruses. The viral particles had a buoyant density of 1.16 g/ml in sucrose gradients and contained a high-molecular-weight RNA and an RNA-instructed DNA polymerase. The viral polymerase was active in an endogenous reaction requiring the presence of the four deoxyriboside triphosphates and manganese ions, and was sensitive to RNase. The DNA product of the endogenous reaction specifically hybridized to P3HR-I viral 60 to 70S RNA. Electron microscopic examination of ultrathin sections of P3HR-I cells revealed immature, mature and budding virions typical of type-C retroviridae. Nucleic acid hybridization assays showed no sequence homoblastosis virus, murine oncornaviruses, simian sarcoma virus or RD114 virus.

Mason-Pfizer like virus in kidney grafted patients

Lymphocytes from a kidney grafted patient were specifically stimulated to incorporated thymidine in vitro by mitomycin C treated Hela cells infected with a Mason-Pfizer like virus (MPV). The thermolabile mutant of vesicular stomatitis virus (VSV tl) grown in leukocytes of this patient produced pseudotypes which were neutralized by the patient's sera and boy rabbit anti-MPV sera. Coculture of the patients leukocytes with SIRC cells yielded virus populations with dual properties; those of MPV plus those of another virus which was not typed serologically but possessed the biological properties of typical C particles. The patient also had neutralizing antibodies to MPV, which were detected by inhibition of syncytium formation on KC cells and by neutralization of VSV tl (MPV) pseudotypes. Preliminary results on the frequency of similar findings in other kidney grafted patients are presented.

Sequences associated with intracisternal A particles are reiterated in the mouse genome

Using a 3H-cDNA for RNA sequences specifically associated with murine intracisternal type A particles, we have found multiple copies of this information in high molecular weight nuclear DNA from tissues of both Mus muscules (BALB/c, NIH Swiss, A/Jax and feral) and Mus cervicolor. Reiteration frequencies varied from 1050-1800 per haploid genome, except that fewer copies (450) were found in BALB/3T3 cells. In the series studied, the reiteration frequencies in the DNA of A particle-rich tumor cells (myeloma and neuroblastoma) were not higher than those in normal tissues (liver and sperm). Multiple copies were retained when cellular DNAs were sedimented through alkaline sucrose gradients, indicating that the sequences are integrated in the mouse genome. In situ hybridization with cDNA showed that the sequences were associated with many chromosomes and were concentrated over certain regions of some chromosomes. Only low levels of homologous sequences were detected in rat, hamster and guinea pig DNA under stringent conditions of hybridization. The presence of reiterated sequence transcripts in poly(A) RNA from a neuroblastoma A particle fraction was confirmed by direct hybridization of the RNA with cellular DNA.

Radioimmunoassay for the major structural protein of Mason-Pfizer monkey virus: Attempts to detect the presence of antigen or antibody in humans

The 25,000 dalton protein of Mason-Pfizer monkey virus (MPMV) was isolated by gel filtration chromatography. In agreement with results from other laboratories, antisera to type-C and the non-type-C bovine leukemia and equine infectious anemia viruses did not precipitate 125I-labelled MPMV p25. In addition, these viruses did not cross-react in a competition radioimmunoassay for MPMV p25. Twenty-one human tissues (15 breast carcinomas, 2 normal breasts, 3 acute myelogenous leukemias and 1 sarcoma) were fractionated by detergent solubilization, ammonium sulfate precipitation, and DE-52 anion exchange chromatography. These methods were shown to be highly effective for purification of MPMV p25. Under assay conditions which minimized incubation damage to the 125I-MPMV p25, all tissues failed to react in the competition radioimmunoassay (RIAT). Two hundred and two human sera or plasma specimens, including those from patients with breast cancer and 33 age-matched controls, from 50 patients with hematologic malignancies, from 12 patients with amyotrophic lateral sclerosis, and from 14 patients with systemic lupus erythematosis, were examined for antibodies to MPMV p25. With the exception of two multiple myeloma plasma which produced artifactual false positive reactions based on hypergammaglobulinemia, a known complication of salt precipitation radioimmunoassays, the remainder of the specimens were negative for evidence of MPMV p25 antibodies.

Phenotypic mixing of vesicular stomatitis virus and D-type oncornavirus

After mixed infection of cells with vesicular stomatitis virus (VSV, thermolabile mutant tl 17) and oncornavirus type D, phenotypically mixed virions are formed containing the VSV genome and oncornavirus and VSV envelope. The virions are thermostable and have serologic characteristics of both viruses.

Characterization of an established cell line (SH-3) derived from pleural effusion of patient with breast cancer

Spontaneous emergence of fast-growing cells in prolonged culture of pleural effusion cells obtained from a patient with breast cancer has led to the establishment of a cell line designated as SH-3. By morphological criteria, as revealed by light and electron microscopy, SH-3 cells are epithelial and resumble the poorly differentiated cells of a series of established human tumor cell lines. Their karyotype is hypotetraploid and different from that of HeLa cells. Isoenzyme analysis has shown the presence in the cells of a bone-type alkaline phosphatase and of the fast (A) band of G6PD. The line is free of mycoplasma.

Mason-Pfizer virus RNA genome: relationship to the RNA of morphologically similar isolates and other oncornaviruses

The 60-70S RNA of Mason-Pfizer virus (MPV) was iodinated in vitro and used in both direct and competitive molecular hybridization studies. MPV proviral sequences are present at a frequency of approximately one to two copies per haploid genome in the DNA of experimentally infected human cells. By nucleic acid competition hybridization, MPV RNA was found to be indistinguishable from the RNA of a virus (X381) isolated from a rhesus mammary gland and from RNA isolated from the cytoplasm of AO cells (Parks et al., 1973) and HeLa cells (Gelderblom et al., 1974), both previously reported to produce MPV-related particles. No homology was observed, however, between MPV RNA and the RNA, or the DNA, from two clones of HeLa cells obtained from the American Type Culture Collection. Hybridization of MPV 60-70S RNA to the DNA of normal tissues of humans and to the DNA of 11 other species revealed that MPV is not an endogenous virus of any of these species. Competition hybridization revealed no detectable sequence homology between the RNA of MPV and the RNAs of simian sarcoma virus, murine mammary tumor virus, murine leukemia virus, BUdR-induced guinea pig virus, or avian myeloblastosis virus. These nucleic acid studies substantiate previous ultrastructural and immunological findings that MPV and morphologically similar isolates constitute a distinct group of oncornavirus.

Terminal dilution purification of adenovirus prototypes, and the antigenic relationship between types 4, 16 and 14

Two terminal dilution purifications in HEK cells were performed with adenovirus prototypes of types 1 to 7, 12, 16, 19 and 9-15, and one terminal dilution with a freshly isolated type 8 strain. The antisera prepared against viruses after terminal dilution neutralized the original and the purified virus to the same extent, indicating the antigenic purity of the respective prototypes. Cross-reactions in neutralization with other types within the subgroup were also identical. Only the prototype of type 16 (Ch 79) showed a cross-neutralization with type 4, while four type 16 wild strains showed cross-neutralization with type 14, but none with type 4. The prototype (CH 79) is a "prime strain" in relation to the type 16 wild strains.

Mason-Pfizer monkey virus: analysis and localization of virion proteins and glycoproteins

The polypeptide composition of Mason-Pfizer monkey virus was determined using sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Six major polypeptides of molecular weights 68,000, 27,000, 20,000, 14,000, 12,000, and 10,000 were resolved regardless of the cell type (i.e., two human and two rhesus) in which the virus was grown. Protein gp68 (68,000) represented the major virus glycoprotein and protein gp20 (20,000) represented a minor glycoprotein of the virion, again regardless of the cell type of origin of the virus. Protein gp68 appears to be located on the outer surface of the viral envelope, as demonstrated by lactoperoxidase catalyzed iodination of intact virions. Additional glycoproteins were shown to be virion associated; their presence depended, however, on the cell type in which the virus was propagated.

Sequence homology between the RNA of Mason-Pfizer monkey virus and the RNA of human malignant breast tumors

Radioactive DNA ([(3)H]cDNA) complementary to the RNA of Mason-Pfizer monkey virus was used in molecular hybridization experiments to demonstrate sequence homology between its viral RNA and RNA of human malignant breast tumors. Hybridization products were analyzed by cesium sulfate equilibrium density centrifugation and hydroxylapatite chromatography. Seven of ten human malignant breast tumors tested contained virus-related RNA when assayed by hydroxylapatite chromatography, whereas no sequence homology was found in RNA from 11 human benign breast tumors or from RNA of normal human spleen, liver, or kidney. Hybridizations between [(3)H]cDNA of the monkey virus and human breast adenocarcinoma RNA showed a C(r)t((1/2)) of about 2 x 10(4). The fidelity of the hybrids formed was indicated by a T(m) of 80.5 degrees .

Immunological properties of two polypeptides of Mason-Pfizer monkey virus

Two polypeptides were isolated from the Mason-Pfizer monkey virus (MP-MV). The polypeptides, designated MP-MV p26 and MP-MV p15, were 26,000 and 15,000 molecular weight, respectively, based on gel filtration chromatography in the presence of 6 M guanidine hydrochloride. Radioimmunoassays developed for MP-MV p26 and p15 were, respectively, 10 and 100 times more sensitive than immunodiffusion and 1 and 10 times more sensitive than micro-complement fixation for the detection of MP-MV. Antigens of other reverse transcriptase-containing RNA viruses did not cross-react in either MP-MV radioimmunoassay. Further, antisera against these other viruses did not react with the radioiodine-labeled MP-MV polypeptides. The MP-MV radioimmunoassays should be useful in studying the natural occurrence of this virus and its relationship to primate tumors.