Primate retroviruses: envelope glycoproteins of endogenous type C and type D viruses possess common interspecies antigenic determinants.

The major 70,000- to 80,000-molecular-weight envelope glycoproteins of the squirrel monkey retrovirus, Mason-Pfizer monkey virus, and M7 baboon virus and the related endogenous feline virus, RD114, were isolated and immunologically characterized. Immunoprecipitation and competition immunoassay analysis revealed these viral envelope glycoproteins to possess several distinct classes of immunological determinants. These include species-specific determinants, group-specific antigenic determinants unique to endogenous primate type C viruses, and group-specific determinants for type D viruses such as Mason-Pfizer monkey virus and squirrel monkey retrovirus. In addition, a class of broadly reactive antigenic determinants shared by envelope glycoproteins of both type C viruses of the baboon/RD114 group and type D viruses of the Mason-Pfizer monkey virus/squirrel monkey virus group are described. Other mammalian oncornaviruses tested, including isolates of nonprimate origin and representative type B viruses, lacked these determinants. The demonstration of antigenic determinants specific to envelope glycoproteins of type C and type D primate viruses indicates either that these viruses are evolutionarily related or that genetic recombination occurred between their progenitors. Alternatively, endogenous type D oncornaviruses may be replication defective, and acquisition of endogenous type C viral genetic sequences coding for envelope glycoprotein determinants may be necessary for their isolation as infectious virus.     

Comparative studies on the structural phosphoproteins of mammalian type C viruses.

The major phosphoprotein common to woolly monkey sarcoma virus, gibbon ape lymphosarcoma virus, and type C viruses of the lower mammalian species (mouse, rat, cat), with the exception of the endogenous cat virus (RD-114), is the polypeptide of about 12,000 molecular weight. The protein-phosphate bond in this polypeptide of several viruses is of the phosphoserine variety excepting gibbon ape virus, which contains both phosphoserine and phosphothreonine. The primary phosphoprotein of RD-114 virus and the endogenous baboon type C virus, on the other hand, is the polypeptide of about 15,000 molecular weight which contains phosphothreonine as its phosphoamino acid. A second major phosphoprotein of molecular weight of 10,000 is detected only in viruses genetically related to rat species including those derived from the RPL cell line, from Sprague-Dawley rat embryo cells, and the Kirsten mouse sarcoma virus which was recovered from a mouse erythroblastosis virus after in vivo propagation through rat. These phosphorylated polypeptides of molecular weight 15,000, 12,000, or 10,000 are present in the virion structure in several different but nonrandom phosphorylated states.     

Structural polypeptides of mammalian type C RNA viruses. Isolation and immunologic characterization of a low molecular weight polypeptide, p10.

Low molecular weight polypeptides of several mammalian type C RNA tumor viruses were purified by sequential ion exchange chromatography and molecular sizing techniques. These included a polypeptide with a molecular weight of 10,000 to 11,000, p 10, from two type C viruses of mouse origin. Rauscher- and Moloney-murine leukemia virus (MuL virus), and from an infectious type C virus isolate of the woolly monkey. The p12 structural polypeptides of these viruses as well as Rauscher-MuL virus p15 were also purified. By using radioimmunoassays developed for each polypeptide, it was possible to demonstrate that all three low molecular weight polypeptides, p15, p12, and p10, were immunologically unique. Among type C viral structural polypeptides, p10 has been least well characterized immunologically. The results of the present study indicate that p10 is virus-coded and possesses strong group-specific antigenic determinants. By use of appropriate immunoassays, broadly reactive interspecies determinants shared by mammalian type C virus isolates of murine, feline, and primate origin, were also demonstrated. The interspecies antigenic determinants of p10 were shown to be as broadly cross-reactive as those exhibited by the major type C virus structural polypeptide, p30.     

Radiommunoassays for the 70,000-molecular-weight glycoproteins of endogenous mouse type C viruses: viral antigen expression in normal mouse tissues and sera.

Genetic information coding for type C RNA viruses is transmitted within the DNA of mouse cells. At least three endogenous viruses have so far been immunologically distinguished by radioimmunoassays for their 12,000-molecular-weight polypeptides (p12). In the present study, the 70,000-molecular-weight glycoproteins (gp70) of three prototype viruses were purified, and competition radioimmunoassays were developed for each. By use of these immunoassays, the antigenic determinants of gp70's of different classes of endogenous virus, isolated from the same and from a variety of other mouse strains, were readily discriminated. In contrast, viruses of the same class were indistinguishable. These findings further document the existence of three distinct endogenous viruses of mouse cell. The levels of type C viral gp70 were quantitated in tissues and sera of several inbred strains. The pattern of immunological reactivity of the gp70 detected in serum was indistinguishable from that of the viral gp70 partially purified from tissues of the same strain. Moreover, in each case it was indistinguishable from that of a specific class of endogenous virus. In virus-negative tissues of BALB/c and NIH Swiss mice, the viral gp70 detected was shown to be representative of a class III endogenous virus whose p12 polypeptide was also expressed by the same cells.     

Evolutionary relationships between gag gene-coded proteins of murine and primate endogenous type C RNA viruses.

Several low molecular weight proteins of endogenous type C viruses of the RD114/baboon group are compared with the gag gene translational products of endogenous type C viruses of murine origin. The p10 proteins of each virus group are shown to be immunologically and biochemically related, while the p12 proteins of RD114/baboon viruses are demonstrated to share antigenic determinants with murine viral p15. Moreover, highly type-specific phosphoproteins, p15 of RD114/baboon viruses and p12 of murine viruses, are shown to possess very similar biochemical properties. These findings, along with previous studies indicating immunologic cross-reactivity between their major internal antigens, p30, demonstrate that each of the gag gene-coded proteins of murine type C viruses has a analogue in viruses of the RD114/baboon group. The immunologic and biochemical relatedness of their gag gene translational products supports the concept of a common progenitor in the evolution of these endogenous viruses.     

Analysis of antigenic determinants of structural polypeptides of avian type C tumor viruses.

Radioimmunoassays were developed for the 19,000, 15,000, and 12,000 molecular weight polypeptides of avian myeloblastosis virus and for the 19,000 and 12,000 polypeptides of RAV-0, a subgroup E avian tumor virus. Each polypeptide was shown to possess both group- and type-specific antigenic determinants, in contrast to the 27,000 mol wt polypeptide, which contained only group-specific determinants. The corresponding low-molecular-weight polypeptides of subgroup A, B, and E viruses were shown to be immunologically indistinguishable. The findings that low-molecular-weight polypeptides of subgroup C and D viruses reacted very differently in immunoassays for the respective polypeptides of avian myeloblastosis virus or RAV-0 suggest that subgroups C and D may have evolved differently form subgroups A, B, and E.     

Two distinct endogenous type C viruses isolated from the asian rodent Mus cervicolor: conservation of virogene sequences in related rodent species.

The cocultivation of a lung cell line from the Southeast Asian mouse Mus cervicolor with cells from heterologous species has resulted in the isolation of two new distinct type C viruses. Both viruses are endogenous to M. cervicolor and are present in multiple copies in the cellular DNA of these mice. One of the viruses, designated M. cervicolor type CI, replicates readily in the SIRC rabbit cell line and is antigenically related to the infectious primate type C viruses isolated from a woolly monkey (simian sarcoma-associated virus) and gibbon apes (gibbon ape leukemia virus). This virus is also closely related by both immunological and nucleic acid hybridization criteria to a type C virus previously isolated from a second Asian murine species, Mus caroli. The isolation of the M. cervicolor type C I virus thus provides further evidence that the infectious primate type C viruses originated by trans-species infection of primates by an endogenous virus of mice. The second virus, designated M. cervicolor type C II, replicates well in various cell lines derived from the laboratory mouse Mus musculus. While antigenically related to type C viruses derived from M. musculus, the M. cervicolor type C II virus isolate can be readily distinguished from standard murine leukemia viruses. Both new type C viruses from M. cervicolor are unrelated to the previously described retrovirus (M432) isolated from the same Mus species. The DNA of M. cervicolor therefore contains multiple copies of at least three distinct classes of endogenous viral genes. An examination of the cellular DNA of other rodent species for nucleic acid sequences related to the genomes of both M. cervicolor type C I and II reveals that both viruses have been highly conserved evolutionarily, and that other species of rodents, such as laboratory mice and rats, contain endogenous virogenes related to those in the DNA of M. cervicolor.     

Type C viruses of baboons: isolation from normal cell cultures

Four new type C viruses were isolated from putatively virus-negative baboon lung, kidney, and testicular cells by cocultivation with several permissive host cell lines. The baboon type C viruses are infectious for cells from various mammalian species, but do not replicate in any baboon cell lines so far tested. These viruses can be distinguished from other major classes of mammalian type C viruses, including previous isolates from primates, but are most closely related to endogenous feline viruses of the RD-114/CCC group. By immunologic criteria, viral host range, and nucleic acid hybridization studies, the baboon type C viruses are highly related to one another and represent a distinct new class of endogenous primate type C viruses.     

Chemical and Immunological characterization of the major structural protein (p28) of MMC-1, a rhesus monkey endogenous type C virus: homology with the major structural protein of avian reticuloendotheliosis virus.

The major core protein (p28) of MMC-1, an endogenous type C virus of the rhesus monkey (Macaca mulatta), was purified and subjected to structural and immunological analyses. The NH2-terminal amino acid sequence of MMC-1 p28 showed extensive homology to the sequences of the major structural proteins (p30) of known mammalian type C viruses. Similarly, interspecies antigenic determinants shared by all the above viral proteins were detected in MMC-1 p28. Competition radioimmunoassays together with the results of statistical analysis of the primary structure data provided evidence that MMC-1 p28 is not more closely related to primate type C viruses of the Papio genus than to those isolated from rodents, cats, or New World monkeys. MMC-1 p28 was found to be closely related structurally to the p30 protein of the avian reticuloendotheliosis virus (REV-A), a horizontally transmitted type C virus of putative mammalian origin. In addition, MMC-1 p28 and REV-A p30 shared a specific subset of antigenic determinants not present in any of the other avian or mammalian type C viruses studied. These findings suggest that MMC-1 and REV may have a common evolutionary origin.     

Structural Proteins of Mammalian Oncogenic RNA Viruses: Immunological Characterization of the p15 Polypeptide of Rauscher Murine Virus

The immunological properties of the purified 15,000-dalton protein of Rauscher murine type-C virus were analyzed by radioimmunoassay. The majority of the antigenic determinants of this protein were found to be remarkably specific to Rauscher and Friend virus and to a lesser extent to Moloney virus. Determinants reactive with other murine viruses (group-specific) or type-C viruses of other species (interspecies) were also demonstrated but were minor components of the total antigenic specificities of the protein. The results provide evidence that the antigenic properties of this protein specify the Friend-Moloney-Rauscher subgroup of type-C viruses.     

Molecular diversity among five different endogenous primate retroviruses.

Genetically transmitted retroviruses of Old and New World monkeys include type C viruses isolated from baboons (M7), macaque (MAC-1), and owl monkeys (OMC-1) and type D viruses from langurs (PO-1-Lu) and squirrel monkeys (SMRV, M534). Each of these isolates is unrelated to the others by nucleic acid hybridization criteria and contains a unique array of virion-associated proteins which can be resolved by agarose gel filtration and polyacrylamide gel electrophoresis under denaturing conditions. The major structural protein of each virus has a distinct primary structure, as determined by two-dimensional tryptic peptide analysis, and is antigenically different from the others. The major virion phosphoproteins of endogenous primate type C viruses (pp15) are also different from those of type D viruses (pp13-pp14). Immunological and structural analyses show that the endogenous langur virus and the horizontally transmitted Mason-Pfizer virus of rhesus monkeys are closely related to one another, consistent with the sequence homology detected in their RNA genomes. Although certain radioimmunoassays detect interspecies antigenic determinants common to either the p30 or gp70 proteins of some of these viruses, no one assay has yet been designed which can detect all groups of endogenous primate retroviridae. The data lead to the conclusion that primates contain a minimum of three different sets of genetically transmitted type C and type D retroviral genes.     

Antigenic determinants of the 70,000 molecular weight glycoprotein of woolly monkey type C RNA virus.

The 70,000 molecular weight glycoprotein (gp70) of a type-C RNA virus originally isolated from a woolly monkey has been partially purified and immunologically characterized. Evidence that this viral protein is viral coded was derived from studies showing its antigenic properties to be unaltered by virus passage in cells of different species. A broadly reactive competition immunoassay was developed utilizing antiserum prepared against feline leukemia virus to precipitate 125I-labeled woolly monkey virus gp70. Gibbon and woolly viruses, as well as feline and several mouse type-C viruses, all reacted with equal efficiency in this assay. In contrast, an endogenous virus of the baboon failed to cross-react, suggesting that viruses of this latter group are less immunologically related to the others. In a homologous competition immunoassay for the woolly viral glycoprotein, the woolly virus was readily distingusihed from otherwise colsely related viruses of gibbon apes. These findings demonstrate the pronounced type-specific antigenic dterminants possessed by this viral protein. The antigenic determinants of gp70 responsible for neutralization have also been investigated.     

Serological studies with low-molecular-weight polypeptides from the Moloney strain of murine leukemia virus.

Major virion low-molecular-weight polypeptides were isolated from the Moloney strain of murine leukemia virus (type C) by agarose chromatography in 6M guanidine hydrochloride and were shown to have molecular weights of 15,000 (p15), 12,000 (p12), and 10,000 (p10) by their elution volumes and by their relative mobilities in sodium dodecyl sulfate-polyacrylamide gels. Each polypeptide could be iodinated and employed in double antibody radioimmunoassay procedures. All three polypeptides demonstrated a high degree of type-specificity in serologic immunoprecipitation analysis and in corresponding competition immunoassays. The p15 was immunologically distinct from other viron polypeptides including p12 and p10; the p12 and p10 were highly related to each other but not to other virion polypeptides and were even more type-specific than the p15 in serologic tests. Competition immunoassays with p15 and p10 indicate that the Moloney strain of MuLV is only a distant relative of the Friend-Rauscher group. The combined use of the Kirsten and Moloney low-molecular-weight polypeptide immunoassays suggest that xenotropic viruses constitute yet another group(s) of murine leukemia virus with distinct type-specific antigens, further expanding an already heterogeneous group of mouse type C viruses.     

Evidence for genetic recombination between endogenous and exogenous mouse RNA type C viruses

Two viruses isolated following prolonged growth of serologically distinct mouse type C RNA viruses in human cells have previously been shown to have acquired common envelope properties distinct from those of either parental virus. Virus neutralization tests show that the viruses selected in human cells possess envelope antigens identical to those of endogenous mouse type C viruses of cells in which the parental viruses had been propagated. In contrast, the p12 polypeptide of each virus selected in human cells is antigenically indistinguishable from that of its respective parental virus and different from those of known endogenous mouse type C viruses. Molecular hybridization indicates significant differences in the genetic sequences of one virus and its parent, excluding the possibility that it arose from a point mutation. These findings indicate that the viruses selected in human cells represent genetic recombinants between exogenous and endogenous mouse type C viruses.