bluuebunny/crossref_metadata_2025 huggingface dataset:
Genetic studies of cell fusion induced by herpes simplex virus type 1
Authors: Read G S , Person S , Keller P M
Published: January 2020

Eight cell fusion-causing syn mutants were isolated from the KOS strain of herpes simplex virus type 1. Unlike the wild-type virus, the mutants produced plaques containing multinucleated cells, or syncytia. Fusion kinetics curves were established with a Coulter Counter assay for the mutants and wild-type virus in single infections of human embryonic lung (HEL) cells, for the mutants and wild-type virus in mixed infections (dominance test), and for pairs of mutants in mixed infections (complementation test). In single infections, fusion began 4 to 6 h after infection and proceeded with an exponential decrease in the number of small single cells. At some later time that was characteristic of the mutant, there was a significant reduction in the rate of fusion for all but possibly one of the mutants. Although the wild-type virus did not produce syncytial plaques, it did induce a small amount of fusion that stopped abruptly about 2 h after it started. These data are consistent with the hypothesis that both mutants and wild type induce an active fusion inducer and that the activity of this inducer is subsequently inhibited. The extent of fusion is apparently determined by the length of the interval during which the fusion inducer is active. That fusion is actively inhibited in wild-type infections is indicated by the observation that syn mutant-infected cells fused more readily with uninfected cells than with wild-type infected cells. Fusion was decreased in mixed infections with the mutants and wild-type virus, but the mutants displayed a codominant fusion phenotype. Fusion was not decreased in mixed infection with pairs of mutants, indicating that the mutants, with one possible exception, are members of the same complementation group. A linkage map was established for six of the mutants by analysis of recombination frequencies.
Replication of Chinese hamster embryo cells transformed by temperature-sensitive T-antigen mutants of simian virus 40
Authors: Robinson C C , Swartzendruber D E , Lehman J M
Published: January 2020

Chinese hamster embryo cells transformed by simian virus 40 temperature-sensitive T-antigen mutants replicated when confluent at 40.5 degrees C, regardless of the selection method, selection temperature, or virus strain used.
Evidence for the common origin of viral and cellular sequences involved in sarcomagenic transformation
Authors: Wang L H , Snyder P , Hanafusa T , Hanafusa H
Published: January 2020

The src genes of six different strains of avian sarcoma virus (ASV) were compared with those of a series of newly isolated sarcoma viruses, termed "recovery avian sarcoma viruses" (rASV's). The rASV's were isolated recently from chicken and quail tumors induced by transformation-defective (td) deletion mutants of Schmidt-Ruppin Rous sarcoma virus. The RNase T1-resistant oligonucleotide maps were constructed for the RNA genomes of different strains of ASV and td mutants. The src-specific sequences, characterized by RNase T1-resistant oligonucleotides ranging from 9 to 19 nucleotides long, were defined as those mapping between approximately 600 and 2,800 nucleotides from the 3' polyadenylate end of individual sarcoma viral RNAs, and missing in the corresponding td viral RNAs. Our results revealed that 12 src-specific oligonucleotides were highly conserved among several strains of ASV, including the rASV's, whereas certain strains of ASV were found to contain one to three characteristic src-specific oligonucleotides. We previously presented evidence supporting the idea that most of the src-specific sequences present in rASV RNAs are derived from cellular genetic information. Our present data indicate that the src genes of rASV's are closely related to other known ASVs. We conclude that the src genes of different strains of ASV and the cellular sarc sequences are of common origin, although some divergence has occurred among different viral src genes and related cellular sequences.
Functional organization of the Harvey murine sarcoma virus genome
Authors: Chang E H , Maryak J M , Wei C M , Shih T Y , Shober R , Cheung H L , Ellis R W , Hager G L , Scolnick E M , Lowy D R
Published: January 2020

The comparative infectivity of Harvey murine sarcoma virus (Ha-MuSV) DNA for NIH 3T3 cells was determined for supercoiled Ha-MuSV DNA molecularly cloned in lambda phage and pBR322 at its unique EcoRI site (which is located near the middle of the 6-kilobase pair [kbp] unintegrated linear viral DNA) and for two cloned subgenomic fragments: one was 3.8 kbp and lacked about 1 kbp from each side of the EcoRI site, and the second did not contain the 3 kbp of the unintegrated linear viral DNA located on the 3' side of the EcoRI site. Each subgenomic DNA induced foci of transformed cells, but with a lower relative efficiency then genomic DNA. Transfection with intact vector Ha-MuSV DNA yielded results similar to those obtained after separation of Ha-MuSV DNA from vector DNA. Cells lines were then derived from individual foci transformed with each type of viral DNA. Focus-forming virus was recovered from transformed cells after superinfection with a helper-independent virus, but the efficiency varied by several orders of magnitude. For several transformed lines, the efficiency of recovery of focus-forming virus was correlated with the structure of the Ha-MuSV DNA in the cells before superinfection. When 32P-labeled Ha-MuSV DNA probes specific for sequences on either the 3' or 5' side of the EcoRI site were used to analyze the viral RNA in the transformed cell lines, all lines were found to hybridize with the 5' probe, but some lines did not hybridize with the 3' probe. The transformed lines contained high levels of the Ha-MuSV-coded p21 or its associated GDP-binding activity. We conclude that the transforming region and the sequences that code for the viral p21 protein are both located within the 2 kilobases closest to the 5' end of the Ha-MuSV genome.
Proviruses of mouse mammary tumor virus in normal and neoplastic tissues from GR and C3Hf mouse strains
Authors: Cohen J C , Varmus H E
Published: January 2020

We analyzed two experimental situations to assess the role of endogenous mouse mammary tumor virus (MMTV) DNA in the genesis of mammary carcinomas. (i) GR mice carry in their germ line one or more proviruses indistinguishable by limited restriction mapping from the proviruses introduced into cells by experimental infection with the highly tumorigenic virus isolated from GR mouse milk, MMTV(GR). Most tumors arising in GR mice contain one or more proviruses at various sites in tumor DNA in addition to those present endogenously. Detection of these new proviruses is possible as a consequence of the clonal or quasiclonal character of the tumors. (ii) C3H/He mice carry three units of endogenous viral DNA, none of which resembles the DNA of the commonly encountered strains of milk-borne MMTV. Nevertheless, MMTV-associated tumors arise late in life when these animals are removed from the influence of milk-borne virus; the responsible agent, MMTV(C3Hf), can also produce tumors in BALB/c mice. We found that tumors arising in both C3Hf/He mice and BALB/c mice infected with MMTV(C3Hf) were clonal or quasiclonal and contained one or more new copies of proviral DNA at various sites in the host genome. These new proviruses were readily distinguished from the proviruses of the common milk-borne virus strains and closely resembled unit II of endogenous MMTV DNA (Cohen et al., J. Virol., 32:483-496). Thus, in both experimental systems, we found evidence for new proviruses in mammary tumors, despite the preexistence of similar or identical proviruses in the germ line. The results suggest that the repositioning of MMTV proviruses may be required for the full expression of the oncogenic potential of endogenous MMTV DNA.
Multiple mRNA species for adenovirus type 2 polypeptides III and pVII
Authors: Lawrence C B
Published: January 2020

Fractionation of messenger activities isolated from the cytoplasm of HeLa cells late in infection with adenovirus type 2 reveals that viral polypeptides III and pVII are each synthesized from two different-sized mRNA's. the major messenger activity for each protein has the same sedimentation rate as that previously reported by Anderson et al. (Proc. Natl. Acad. Sci. U.S.A. 71:2756-2760, 1974). The minor messenger activities for III and pVII sediment more rapidly and are not aggregates of the major mRNA's for these proteins. The two minor messenger activities cosediment with two polyadenylated RNA species which are labeled late in infection with 32P and whose molecular weights are estimated to be 2.9 x 10(6) and 2.4 x 10(6). Both of these species hybridize to adenovirus type 2 DNA specific for the mRNA family that is 3' coterminal at adenovirus type 2 map position 49.5 and the mRNA family that is 3' coterminal at 62.0. This is consistent with the possibility that these RNAs have 5'-terminal sequences identical to those of the normal mRNA's for III and pVII but are 3' coterminal at map position 62, the normal 3' terminus of the mRNA's for polypeptides II and pVI. These species are not found in polyadenylated RNA isolated from the nucleus, suggesting that the minor mRNA species are cytoplasmic RNAs.
Free viral DNA in BK virus-induced hamster tumor cells
Authors: ter Schegget J , Voves J , van Strien A , van der Noordaa J
Published: January 2020

The biological properties of nine clonal lines of BK virus-induced hamster tumor cells were studied. All clonal lines were oncogenic and showed an enhanced ability to form colonies in semisolid medium. The cells of each clonal line contained T antigen; no virus could be rescued from any of the clonal lines. The number of viral DNA copies was determined in three of the clonal lines and varied from 10 to 20 copies per diploid amount of cell DNA. The state of the viral genome was studied in these lines, and the great majority of the viral DNA molecules appeared to be present as free (nonintegrated) molecules. At least six length classes of free defective BK virus DNA molecules, which all lacked a part of the late region of the genome, were detected in these cells. Three of the six length classes of BK virus DNA molecules acquired a TaqI recognition site, which suggested substitution of cellular DNA.
Picornaviral VPg sequences are contained in the replicase precursor
Authors: Pallansch M A , Kew O M , Palmenberg A C , Golini F , Wimmer E , Rueckert R R
Published: January 2020

It has previously been shown that the RNA replicase of encephalomyocarditis virus contains two virus-coded proteins, D and E, which are produced in two successive proteolytic steps: (i) C leads to D + ?; and (ii) D leads to p22 + E. It is here shown (i) that virus protein H (molecular weight, 12,000) is the previously unidentified product of the first step and (ii) that VPg, a protein linked covalently to the virion RNA, yields two tryptic peptides found in protein C but not in protein D. The results suggest that VPg is derived by cleavage of protein C and that protein H may be intermediate. Preliminary experiments with VPg sequences in polioviral noncapsid protein 1b, the counterpart of encephalomyocarditis viral protein C, were inconclusive.
Spontaneous Conversion of Nontransformed Avian Sarcoma Virus-Infected Rat Cells to the Transformed Phenotype
Authors: Turek Lubomir P. , Oppermann Hermann
Published: January 2020

Normal rat kidney (NRK) fibroblasts were infected with the Schmidt-Ruppin strain (SR-D) of avian sarcoma virus (ASV) and cloned 20 h after infection without selection for the transformed phenotype. Most infected clones initially exhibited the flat, nontransformed morphology that is characteristic of uninfected NRK cells. In long-term culture, however, the majority of the SR-D NRK clones began segregating typical ASV-transformed cells. Transforming ASV could be rescued by fusion with chicken embryo fibroblasts from most of the infected clones tested. Three predominantly flat, independently infected clones were further analyzed by subcloning 8 to 10 weeks after infection. Most flat progeny subclones derived at random from two of these “parental” SR-D NRK clonal lines did not yield virus upon fusion with chicken embryo fibroblasts, although a nondefective transforming ASV was repeatedly recovered from the parental clones. This observation suggested that most, but not all, daughter cells in these SR-D NRK clones lost the ASV provirus after cloning. The progeny of the third independent parental cell clone, c17, gave rise to both flat and transformed subclones that carried ASV. In this case, ASV recovery by fusion and transfection from the progeny subclones was equally efficient regardless of the transformation phenotype of the cells. The 60,000-dalton phosphoprotein product of the ASV
src
gene was, however, expressed at high level only in the transformed variants. The results of a Luria-Delbruck fluctuation analysis and of Newcombe's respreading test indicated that the event leading to the spontaneous conversion to the transformed state occurred at random in dividing cultures of these flat ASV NRK cells at a rate predicted for somatic mutation.
Frequent site-specific deletion of coliphage lambda murine sarcoma virus recombinants and its use in the identification of a retrovirus integration site
Authors: McClements W L , Enquist L W , Oskarsson M , Sullivan M , Vande Woude G F
Published: January 2020

Stocks of hybrid lambda phages carrying the complete integrated provirus of either m1 or HT1 Moloney murine sarcoma virus, as well as flanking host sequences, frequently contain significant numbers of phages carrying a specific deletion. This deletion arises from a recombination event between the terminally repeated sequences in the provirus that deletes the unique Moloney murine sarcoma virus sequences bracketed by the terminally repeated sequences. Physical mapping has shown that the deletion phage retains one complete copy of the terminally repeated sequence and the flanking mink host sequences. One such deletion, lambdaHT1r+, was used to characterize a mink genomic DNA sequence that contains an HT1 Moloney murine sarcoma virus integration site. This integration site sequence from normal mink cells was also cloned into phage lambda. An analysis of the heteroduplexes between the integration site and the lambdaHT1r+ deletion indicated that no major rearrangement of host sequences occurred upon integration of the Moloney murine sarcoma provirus.
Transcripts of the adenovirus-associated virus genome: multiple polyadenylated RNAs including a potential primary transcript
Authors: Green M R , Straus S E , Roeder R G
Published: January 2020

Adenovirus-associated virus type 2 synthesizes four prominent viral transcripts, containing 4.3, 3.6, 2.6, and 2.3 kilobases (kb), in productively infected human KB cells (coinfected with adenovirus type 2). All species are polyadenylated and present in both nuclear and whole-cell RNA preparations, but only the predominant 2.3-kb (and possibly the 2.6-kb) RNA species are found on polysomes. Electrophoretic analyses under denaturing conditions of S1 nuclease-generated and exonuclease VII-generated DNA-RNA hybrids revealed, in each case, four protected DNA fragments which are equal in length (within 50 to 100 nucleotides) to the four S1 nuclease-generated hybrids resolved by electrophoresis under nondenaturing conditions. These results suggest that in the infected cell, abundant adenovirus-associated virus type 2 transcripts are present predominantly (by mass) as unspliced RNAs or, alternatively, they are spliced but contain very short (less than or equal to 50 nucleotides) leader sequences. That the 2.3-kb RNA represents such a spliced transcript is suggested by exonuclease VII mapping experiments and our more detailed RNA mapping studies (M. R. Green and R. G. Roeder, J. Virol., in press).
Stimulation of encephalomyocarditis virus RNA translation in wheat embryo extracts by rabbit reticulocyte ribosomal wash
Authors: Shih D S , Shih C Y , Kaesberg P
Published: January 2020

Encephalomyocarditis virus RNA induced a low level of amino acid incorporation in wheat embryo extracts, but the incorporation did not result in the formation of any viral proteins. However, if wheat embryo extracts were supplemented with a ribosomal wash fraction from rabbit reticulocytes, a large stimulation of amino acid incorporation and the formation of encephalomyocarditis virus-specific proteins were obtained. Among the proteins synthesized were capsid precursor proteins which can be processed by an encephalomyocarditis virus-coded protease to produce the viral capsid proteins.
Genomic Masking and Rescue of Dual-Tropic Murine Leukemia Viruses: Role of Pseudotype Virions in Viral Lymphomagenesis
Authors: Haas Martin , Patch Virginia
Published: January 2020

The kinetics of genomic masking of nondefective dual-tropic murine leukemia viruses (MuLV) by ecotropic MuLV in mixedly infected mouse cells was studied. The ratio of virus infection (ecotropic to dual-tropic) determined the kinetics of genomic masking. Some dual-tropic virus isolates could be masked routinely (i.e., converted to virions containing a dual-tropic genome and possessing the ecotropic host range) at all ratios of initial infection of mixedly infected mouse cells. The masked genomes could be rescued as infectious viruses of dual-tropic genotype and host range by an infectious center assay of the infected mouse cells on mink lung cells. Infectious center rescue of masked dual-tropic MuLV took place readily, even from cells that had been kept in continuous culture for many months after the onset of genomic masking. Some dual-tropic virus clones did not undergo genomic masking at any infection ratio with ecotropic virus. Nevertheless, such mixedly infected cultures also gave rise to phenotypically mixed virions, which contained a dual-tropic genome and had an ecotropic host range. (The phenotypically mixed virions found among the progeny of mixedly infected mouse cells were not pseudotypes, as both types of viruses were genetically nondefective, nor was the process leading to their generation a bona fide phenotypic mixing [Fischinger et al., Science 201:457-459, 1978]. Nevertheless, in this paper we use the terms pseudotype and phenotypic mixing because of the lack of a better description.) The lymphomagenic potential of dual-tropic lymphomagenic MuLV was compared with that of phenotypically mixed virions possessing an ecotropic host range and with that of a simple mixture of dual-tropic and ecotropic viruses. The phenotypically mixed pseudotype virions were more potent lymphoma inducers than were those of dual-tropic, cloned genotype. Inoculation of a simple mixture of the viruses did not increase dual-tropic virus tumorigenicity. The reason for this was probably the highly efficient inactivation of dual-tropic virus by oncovirus-inactivating factor, which is present in normal mouse serum and did not inactivate the phenotypically mixed virions. Simple mixtures of dual-tropic lymphomagenic and ecotropic virus preparations behaved like the cloned, dual-tropic virus in vivo and were equally sensitive to oncovirus-inactivating factor in vitro. Thus, phenotypic mixing of dual-tropic and ecotropic MuLV with or without concomitant genomic masking may be a highly significant phenomenon in naturally occurring lymphomagenesis. It may also be important to use phenotypically mixed viruses in the procedures used for in vivo testing of lymphomagenic dual-tropic MuLV isolates.
Recovery of biologically active spleen focus-forming virus from molecularly cloned spleen focus-forming virus-pBR322 circular DNA by cotransfection with infectious type C retroviral DNA
Authors: Linemeyer D L , Ruscetti S K , Menke J G , Scolnick E M
Published: January 2020

The genome of the Lilly-Steeves strain of spleen focus-forming virus (SFFV) was molecularly cloned in the plasmid vector pBR322. Infectious SFFV could be recovered by releasing the SFFV DNA from the vector, transfecting the released DNA onto NIH 3T3 cells, and rescuing the SFFV either by superinfection with helper virus or by cotransfection with molecularly cloned infectious helper viral DNA. By using transfections with SFFV DNA still attached to the plasmid vector, infectious SFFV activity could also be recovered with either method of rescue. Studies performed with these latter types of transfections indicated that only a portion of the SFFV genome was required for biological activity. Since gp52, a marker protein for SFFV, could be detected in all cultures from which adequate titers of biologically active SFFV were recovered, the results are consistent with the hypothesis that gp52 is necessary for SFFV-induced erythroblastosis and polycythemia.
Characterization of the 5'-terminal cap structures of early simian virus 40 mRNA
Authors: Haegeman G , Fiers W
Published: January 2020

Early simian virus 40-specific mRNA was isolated from lytically infected and stably transformed cells and analyzed with respect to the 5'-terminal cap content. An analogous diversity of capped structures was found in both RNA preparations, indicating that 5'-terminal heterogeneity is not limited to late simian virus 40 RNA transcription but concerns a more general feature. Correlation of our data with previously published results of characterization of early mRNA's by reverse transcription allowed a tentative localization of the major 5' termini on the viral genome.
Genetic control of prophage induction in haemophilus influenzae after exposure to psoralen plus near-UV light
Authors: George M , Notani N K
Published: January 2020

Prophage S2 could be induced by psoralen plus near-UV light (PNUV) from a wild-type strain of Haemophilus influenzae, from UV light-sensitive strains uvr-1 and uvr-2 and PNUV-sensitive strains PSO1 amd PSO7, but not from a recombination-deficient strain, rec-1. The levels of prophage induction were comparable in the wild type and an ATP-dependent DNase-deficient strain, KW31, even though the PNUV-induced degradation in the latter strain was considerably lower. Prophage induction could be observed even with chloramphenicol present before, during, and 30 min after PNUV treatment.
Fine-structure mapping and functional analysis of temperature-sensitive mutants in the gene encoding the herpes simplex virus type 1 immediate early protein VP175
Authors: Dixon R A , Schaffer P A
Published: January 2020

Herpes simplex virus (HSV)-specific proteins fall into at least three kinetic classes whose synthesis is sequentially and coordinaely regulated. Temperature-sensitive (ts) mutants of one complementation group (1-2) are defective in the transition from immediate early to early and late protein synthesis. To elucidate the function of the 1-2 gene product in the HSV type 1 replicative cycle, nine ts mutants in this group were mapped by fine-structure analysis and characterized members of the group lie within the terminally repeated sequences of the S region of the genome. Fine-structure genetic and physical mapping permitted the mutations to be ordered within these sequences. Because it has been shown that the message for VP175 and the DNA template specifying this protein extend beyond the limits of the physical map of the mutations, it follows that the mutations must lie within the structural gene for VP175. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis showed that most members of the group overproduced the immediate early proteins VP175, -136, -110, and -63 and markedly underproduced early and late proteins at the nonpermissive temperature. In temperature shiftup experiments, it was fund that the synthesis of early and late proteins ceased, whereas the synthesis of immediate early proteins began again. Thus, it is postulated that VP175 is (i) involved in the transition from immediate early to early protein synthesis, (ii) requird continuously to maintain early protein synthesis, (iii) autoregulated, acting to inhibit immediate early protein synthesis.
Probable localization of the bacteriophage T4 prehead proteinase zymogen in the center of the prehead core
Authors: van Driel R , Traub F , Showe M K
Published: January 2020

During the assembly of the bacteriophage T4 prehead, a T4-coded protease zymogen (P21) is built into the structure. At a certain stage in head formation, the protease precursor is activated and specifically cleaves most of the prehead proteins. In this paper we show that a correlation existed between the presence of proteinaceous material in the center of the prehead core, observed by electron microscopy, and the availability of P21 during prehead assembly. In the absence of P21, the core enclosed a hold of about 35 nm long and 20 nm wide. We found the same for (i) in vitro-assembled, negatively stained prehead-like structures and (ii) in vivo-formed preheads in thin sections of T4-infected cells. We concluded that P21 was localized in the center of the prehead core.
Densonucleosis Virus Structural Proteins
Authors: Kelly D. C. , Moore N. F. , Spilling C. R. , Barwise A. H. , Walker I. O.
Published: January 2020

The protein coats of two densonucleosis viruses (types 1 and 2) were examined by a variety of biophysical, biochemical, and serological techniques. The viruses were 24 nm in diameter, contained at least four polypeptides, were remarkably stable to extremes of pH and denaturing agents, and were serologically closely related. The two viruses could, however, be distinguished serologically and by differences in migration of their structural polypeptides. For each virus the “top component” (i.e., the protein coat minus DNA, found occurring naturally in infections) appeared to have a composition identical to that of the coat of the virus and was a more stable structure. Electrometric titration curves of the virus particles and top components demonstrated that the DNA phosphate in densonucleosis virus particles was neutralized by cations other than basic amino acid side chains of the protein coat. Circular dichroism studies showed that there was a conformational difference between the protein coats of top components and virus particles.
Adsorption, capping, and release of a complex bacteriophage by mycoplasma cells
Authors: Haberer K , Maniloff J , Gerling D
Published: January 2020

By electron microscopic studies, the adsorption and release of nonlytic, cytocidal mycoplasma virus MVL3, which infects ACholeplasma laidlawii cells, have been examined. The MVL3 virion has a polyhedral head, collar, short tail, and tail fibers and contains linear double-stranded DNA. Adsorbed MVL3 virus showed a temperature-dependent clustering or capping on the mycoplasma cell membrane. During infection, a number of virus-cell membrane-related structures were observed, suggesting a general model in which MVL3-infected cells release progeny virions in membrane vesicles. These vesicles must then break down to release MVL3 particles.
Identification of the avian myeloblastosis virus genome. I. Identification of restriction endonuclease fragments associated with acute myeloblastic leukemia
Authors: Souza L M , Baluda M A
Published: January 2020

The proviral DNA of chicken peripheral blood leukemic myeloblasts was analyzed by restriction endonuclease digestion and Southern blotting. Two restriction endonuclease-generated fragments, an EcoRI 2.2-megadalton (Md) and a HindIII 2.6-Md fragment, were present upon enzyme cleavage of all leukemic myeloblast DNA preparations in addition to endogenous or helper-specific fragments. Neither of these fragments was derived from viral DNA of the two known myeloblastosis-associated viruses (MAV-1 and MAV-2). In contrast, DNA similarly treated from the erythrocytes of leukemic chickens showed only small amounts of the two avian myeloblastosis virus-specific fragments, whereas the helper virus-specific fragments were present in the amount seen in MAV-producing chicken embryo fibroblasts. The appearance of the EcoRI 2.2-Md and HindIII 2.6-Md specific fragments in all leukemic myeloblast DNA preparations indicates they are presumably part of the leukemogenic genome that must be present to induce acute myeloblastic leukemia.
Identification of the avian myeloblastosis virus genome. II. Restriction endonuclease analysis of DNA from lambda proviral recombinants and leukemic myeoblast clones
Authors: Souza L M , Briskin M J , Hillyard R L , Baluda M A
Published: January 2020

Two lambda proviral DNA recombinants were characterized with a number of restriction endonucleases. One recombinant contained a complete presumptive avian myeloblastosis virus (AMV) provirus flanked by cellular sequences on either side, and the second recombinant contained 85% of a myeloblastosis-associated virus type 1 (MAV-1)-like provirus with cellular sequences adjacent to the 5' end of the provirus. Comparing the restriction maps for the proviral DNAs contained in each lambda hybrid showed that the putative AMV and MAV-1-like genomes shared identical enzyme sites for 3.6 megadaltons beginning at the 5' termini of the proviruses with respect to viral RNA. Two enzyme sites near the 3'-end of the MAV-1-like provirus were not present in the putative AMV genome. We also examined a number of leukemic myeloblast clones for proviral content and cell-provirus integration sites. The presumptive AMV provirus was present in all the leukemic myeloblast clones regardless of the endogenous proviral content of the target cells or the AMV pseudotype used for conversion. Multiple cellular sites were suitable for integration of the putative AMV genome and the helper genomes. The proviral genomes were all integrated colinearly with respect to linear viral DNA.
Dual evolutionary origin for the rat genetic sequences of Harvey murine sarcoma virus
Authors: Ellis R W , DeFeo D , Maryak J M , Young H A , Shih T Y , Chang E H , Lowy D R , Scolnick E M
Published: January 2020

Detailed restriction endonuclease maps were developed for Harvey murine sarcoma virus (Ha-MuSV) DNA (clone H-1), molecularly closed at its unique EcoRI site in pBR322, for three nonoverlapping subgenomic HindIII clones which together span the entire H-1 clone and for a molecularly cloned DNA copy of a portion of rat 30S RNA (which represents the majority of the rat genetic sequences in Ha-MuSV). Molecular hybridization of the 30S clone to small restriction fragments of clone H-1 revealed a 0.9-to-1.0-kilobase pair region in the 5' half of the Ha-MuSV genome not homologous to the 30S clone, although the 30S clone did contain related sequences in Ha-MuSV on both sides of this nonhomologous region. By using cloned sequences from a segment of the Ha-MuSV nonhomology region as a probe for hybridization to Southern blots of DNA from rat, mouse, bat, and chicken cells, one to three bands were detected in DNA of each species. By contrast, the 30S clone DNA was highly related to many sequences in rat DNA, partially related to fewer mouse DNA sequences, and homologous only to one to three bands in bat and chicken DNA. Earlier work had shown that the 5' half of the Ha-MuSV genome coded for transformation and for the viral p21 protein (Chang et al., J. Virol. 35: 76--92, 1980; Wei et al., Proc. Natl. Acad. Sci. U.S.A., in press). We used two subgenomic HindIII clones whose shared HindIII site mapped within the 5' region of clone H-1 nonhomologous to the 30S clone to test whether the nonhomologous segment might encode the transforming and p21 functions. Although neither of the subgenomic HindIII fragments by themselves induced transformation, ligation of these two nontransforming DNAs to each other did restore p21-mediated transformation. A conclusion consistent with these results is that a region in the 5' half of the Ha-MuSV genome evolutionarily distinct from and not present in rat 30S RNA is essential for transformation and for p21 encoding.
Close similarity between endogenous ecotropic virus of Mus musculus molossinus and AKR virus
Authors: Chattopadhyay S K , Lander M R , Rowe W P
Published: January 2020

By using seven different restriction endonucleases, the cleavage patterns of the unintegrated provioral DNA from an ecotropic murine leukemia virus isolated from Mus musculus molossinus were found to be identical to those of AKR virus. An AKR [3H]DNA probe can be completely saturated with M. musculus molossinus and M. musculus castaneus DNAs, although the arrangement of viral sequences in M. musculus molossinus DNA differed from that of AKR virus. These studies indicate that an AKR-type ecotropic virus is present in some wild Asiatic mice.
BALB/c myeloma retroviruses have mink cell focus-inducing activity
Authors: Spriggs D R , Diebold M A , Krueger R G
Published: January 2020

We have determined the in vitro host range of the cloned MO-21 and FL-1 murine myeloma retroviruses grown in SC-1 cells that were originally isolated from cloned MOPC-21 and FLOPC-1 BALB/c plasmacytoma cell lines. These viruses are able to replicate in murine (BALB/3T3, NIH/3T3) as well as numerous heterologous cell lines. These myeloma retroviruses also exhibit mink cell focus-inducing activity. MO-21 and FL-1 shared interference patterns with each other, but their replication was not interfered with by ecotropic, xenotropic, or amphotropic viruses. The lack of cross-interference with ecotropic or xenotropic viruses distinguishes these isolates from other mink cell focus-inducing viruses.
Molecular cloning of the avian erythroblastosis virus genome and recovery of oncogenic virus by transfection of chicken cells
Authors: Vennström B , Fanshier L , Moscovici C , Bishop J M
Published: January 2020

Avian erythroblastosis virus (AEV) causes erythroblastosis and sarcomas in birds and transforms both erythroblasts and fibroblasts to neoplastic phenotypes in culture. The viral genetic locus required for oncogenesis by AEV is at present poorly defined; moreover, we know very little of the mechanism of tumorigenesis by the virus. To facilitate further analysis of these problems, we used molecular cloning to isolate the genome of AEV as recombinant DNA in a procaryotic vector. The identity of the isolated DNA was verified by mapping with restriction endonucleases and by tests for biological activity. The circular form of unintegrated AEV DNA was purified from synchronously infected quail cells and cloned into the EcoRI site of lambda gtWES x B. A restriction endonuclease cleavage map was established. By hybridization with complementary DNA probes representing specific parts of avian retrovirus genomes, the restriction map of the cloned AEV DNAs was correlated with a genetic map. These data show that nucleotide sequences unique to AEV comprise at least 50% of the genome and are located approximately in the middle of the AEV genome. Our data confirm and extend previous descriptions of the AEV genome obtained by other procedures. We studied in detail two recombinant clones containing AEV DNA: the topography of the viral DNA in the two clones was virtually identical, except that one clone apparently contained two copies of the terminal redundancy that occurs in linear viral DNA isolated from infected cells; the other clone probably contained only one copy of the redundant sequence. To recover infectious virus from the cloned DNA, we developed a procedure for transfection that compensated for the defectiveness of AEV in replication. We accomplished this by ligating cloned AEV DNA to the cloned DNA of a retrovirus (Rous-associated virus type 1) whose genome could complement the deficiencies of AEV. Ligation of the two viral DNAs was facilitated by using a neutral fragment of DNA as linker between otherwise noncompatible termini. Cloned AEV DNA gave rise to infectious AEV capable of transforming fibroblasts and bone marrow cells in culture and of inducing both sarcomas and erythroleukemia in chickens. We conclude that the cloned DNAs represent the authentic genome of AEV undisturbed by the cloning procedure. Molecular cloning offers a powerful approach to the identification and characterization of retrovirus genomes.
New deletion mutant of bacteriophage T5
Authors: Rhoades M , Schwartz J , Wahl J M
Published: January 2020

Deletion mutants of bacteriphage T5 can be identified by analyzing the DNA content of single plaques, after alkaline denaturation, by agarose gel electrophoresis. Use of this procedure has resulted in the isolation of a new mutant, designated del2, that lacks a 1.6% segment located 68 to 70% from the left end of T5 DNA. This segment occurs between the early and late gene regions of T5 DNA.
Physical map of infectious baboon type C viral DNA and sites of integration in infected cells
Authors: Battula N , Todaro G J
Published: January 2020

Three species of unintegrated viral DNAs were found in permissive cells infected with baboon type C virus. The major species was a 9.0-kilobase (kb) linear DNA that was infectious. A restriction endonuclease map of this DNA was constructed and oriented with respect to the viral RNA. The linear DNA had a 0.6-kb sequence repeated at each terminus. These terminal repeat sequences were required for infectivity of the viral DNA. The minor species of the unintegrated viral DNAs were covalently closed circles of 9.0 and 8.4 kb. The smaller circle was in two- to threefold excess over the larger circle. The difference appeared to be that the smaller circle lacked one of the two 0.6-kb repeat sequences found in the larger circle. Restriction endonuclease maps of the integrated viral DNAs were constructed, and the sequences on both viral DNA and cellular DNA that are involved in integration were determined. The integrated viral DNA map was identical to that of the unintegrated infectious 9.0-kb linear DNA. Therefore, a specific site in the terminal repeat sequence of the viral DNA was used to integrate with the host cell DNA. The sizes of the cellular DNA fragments were different from clone to clone but stable with cell passage. Therefore, many sites in the cell DNA can recombine with the viral DNA.
Abelson murine leukemia virus mutants deficient in kinase activity and lymphoid cell transformation
Authors: Rosenberg N E , Clark D R , Witte O N
Published: January 2020

Abelson murine leukemia virus transforms both lymphoid cells and fibroblasts in vitro and induces a unique type of thymus-dependent lymphoma in vivo. Four fibroblast-transforming strains of Abelson murine leukemia virus were identified, based on the sizes of the Abelson murine leukemia virus-specific phosphoproteins produced by these isolates. Two of these strains, the standard P120- and the P160-producing viruses, transformed lymphoid cells efficiently in vitro and induced Abelson disease in vivo. Two other strains, which synthesized small Abelson murine leukemia virus-specific proteins with molecular weights of 90,000 (P90) and 100,000 (P100), transformed lymphoid cells very poorly both in vitro and in vivo. The reduced oncogenic potentials of these isolates were correlated with a high level of synthesis of fairly unstable P90 and P100. In addition, neither P90 nor P100 functional efficiently in protein kinase assays. The correlation of abnormal metabolism and deficient protein kinase activity with the reduced oncogenic potentials of these virus strains supported a direct role for these proteins and the kinase activity in transformation. Furthermore, these results suggested that the requirements for lymphoid cell transformation and fibroblast transformation are different.
Virus of Pekin ducks with structural and biological relatedness to human hepatitis B virus
Authors: Mason W S , Seal G , Summers J
Published: January 2020

A virus found in the sera of Pekin ducks appears to be a new member of the human hepatitis B-like family of viruses. This virus had a diameter of 40 nm and an appearance in the electron microscope similar to that of human hepatitis B virus. The DNA genome of the virus was circular and partially single stranded, and an endogenous DNA polymerase associated with the virus was capable of converting the genome to a double-stranded circle with a size of ca. 3,000 base pairs. An analysis for viral DNA in the organs of infected birds indicated preferential localization in the liver, implicating this organ as the site of virus replication. In all of these aspects, the virus bears a striking resemblance to human hepatitis B virus and appears to be a new member of this family, which also includes ground squirrel hepatitis virus and woodchuck hepatitis virus.
Comparative study of rabies virus persistence in human and hamster cell lines
Authors: Andzhaparidze O G , Bogomolova N N , Boriskin Y S , Bektemirova M S , Drynov I D
Published: January 2020

Persistent infections by rabies virus in BHK-21/13S and HEp-2 cells were studied comparatively. No evidence of interferon production, selection of virus-resistant cells, or integration of the viral genome could be found. Persisting viruses replicated efficiently at 34, 36, and 40 degrees C. Both persistently infected cultures released defective interfering virus particles. A cyclical pattern of infection, which was not characteristic of the persistently infected HEp-2 system, was observed in persistently infected BHK cultures. The virus from persistently infected BHK cultures lost its virulence for mice, whereas the virus from persistently infected HEp-2 cultures retained mouse-killing capacity for more than 3 years.
Host cell factors involved in the production of slowly sedimenting nucleocapsids in measles virus-infected cells
Authors: Bedows E , Payne F E
Published: January 2020

A decrease in the sedimentation rates of the measles virus nucleocapsid, and the RNA contained within, were observed during acute measles virus infection when the growth conditions of Vero cells were altered. The change in sedimentation rates of virus nucleocapsids in these experiments was apparently due to the physiological state of the cell and was independent of the history of the measles virus used for infection since: (i) the same virus stock was used to infect cells from which nucleocapsids were prepared, (ii) nucleocapsid sedimentation rates were rapid when Vero cells freshly revived from liquid nitrogen were infected, but nucleocapsid profiles showed no decrease in the amount of slowly sedimenting material using the same cells and changing the virus preparation used for infection. Frequent cell splittings and numerous medium changes were among the growth factors which appeared to correlate to slowly sedimenting particle production. Changes in the amount of self-complementarity of the measles virus RNA were also observed under these conditions.
Viral DNA synthesized in vitro by avian retrovirus particles permeabilized with melittin. I. Kinetics of synthesis and size of minus- and plus-strand transcripts
Authors: Boone L R , Skalka A M
Published: January 2020

We have examined the kinetics of synthesis of minus [(-)]- and plus [(+)]-strand viral DNA in melittin-permeabilized avian retrovirus particles. The reaction was biphasic. There was a very rapid initial rate, followed, after approximately 1 h, by a lower rate. Many discrete bands of subgenomic-length (-) strands were produced after 10 and 20 min of synthesis; genome-length (7.7-kilobase [kb]) (-) strands were detected within 30 min. Extension to an 8.0-kb (-)-strand species was evident by 60 min. This extension was inhibited by actinomycin D. Synthesis of (+) strands (which is also inhibited by actinomycin D) began early, before any (-) strands were completed, and continued for more than 4 h beyond the time when synthesis of full-length DNA had terminated. Two distinct species of (+)-strand DNA, 0.27 and 0.35 kb, could be observed at the earliest times. Their presence was quickly obscured by subsequent formation of (+)-strand molecules of molecular length between 0.2 and 2.0 kb.
Regulatory and coding potential of the mouse mammary tumor virus long terminal redundancy
Authors: Donehower L A , Huang A L , Hager G L
Published: January 2020

Molecular clones containing the 3' half of newly integrated mouse mammary tumor virus (MMTV) DNA with adjacent mouse cellular sequences were characterized. In addition, we cloned the long terminal redundancy joint from the unintegrated circular form of MMTV DNA. The entire nucleotide sequence of the integrated and part of the unintegrated terminal redundancy was determined; this allowed us to delineate the boundaries of the MMTV long terminal redundancy, which comprises 1,327 base pairs. The position of possible RNA polymerase II initiation and termination signals corresponded closely to the expected regions of viral RNA initiation and termination specified by current models. The MMTV long terminal redundancy also contained a large open reading frame with sufficient information for a protein of 198 amino acids. Initial comparison of flanking 3' cellular sequences from three independent integrated clones suggested there was no host sequence specificity in the MMTV integration event. However, specificity of integration with respect to viral sequences was precise.
Identification of the P proteins and other disulfide-linked and phosphorylated proteins of Newcastle disease virus
Authors: Smith G W , Hightower L E
Published: January 2020

A unique abundant protein, designated P by analogy to the putative polymerase proteins of other paramyxoviruses, was identified in purified Newcastle disease virus. Under nonreducing conditions the P proteins could be separated from other viral proteins on sodium dodecyl sulfate-polyacrylamide gels. The P proteins were isolated from detergent-solubilized virions as 53,000- to 55,000-dalton monomers and disulfide-linked trimers. Distinct forms of P having four different isoelectric points and two different electrophoretic mobilities were resolved by two-dimensional electrophoresis. Two forms of P were phosphorylated, as were the nucleocapsid protein and non-glycosylated membrane protein. In addition to disulfide-linked forms of P, dimers of the hemagglutinin-neuraminidase glycoprotein and two disulfide-linked versions of the fusion glycoprotein were identified. Several electrophoretic variants of the nucleocapsid protein that were probably created by intrachain disulfide bonding were also isolated from virions under nonreducing conditions. The locations of the newly identified proteins were determined by detergent-salt fractionation of virions and by surface-selective radioiodination of the viral envelope. The P proteins were associated with nucleocapsids and were not detected at the surface of virions. Both forms of the fusion glycoproteins were on the exterior of the viral envelope. Herein the properties of the P proteins are compared with similar proteins of rhabdoviruses and other paramyxoviruses, and a role for multiple forms of proteins in the genetic economy of newcastle disease virus is discussed.
In vitro synthesis of adenovirus type 5 T antigens. I. Translation of early region 1-specific rna from lytically infected cells
Authors: Lupker J H , Davis A , Jochemsen H , van der Eb A J
Published: January 2020

Translation of early RNA specific for the leftmost early region 1 of adenovirus type 5 DNA in a rabbit reticulocyte cell-free system resulted in the synthesis of proteins with the following molecular weights: 65,000 (65K), 54K, 42 to 34K, 29K, 25K, 19K, and 18K. All of these proteins could be immunoprecipitated with hamster antitumor serum. The 42 to 34K proteins mapped in early region 1a, and those with molecular weights of 65K, 19K, and 18K mapped in early region 1b. The gene coding for the 54K protein may be localized outside of early region 1. We could not map unambiguously the 29K and 25K proteins. The identification of a 65K protein among products synthesized in vitro suggests that this protein may be identical to the 65K major T antigen present in adenovirus type 5-infected and -transformed cells, and this indicates that it is indeed encoded by the viral genome. This protein is encoded by a 23S mRNA. The other early region 1-specific proteins appear to be encoded by mRNA of approximately 13S, except for the 19K protein, which is synthesized with RNA sedimenting at both 13S and 23S.