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Defective endogenous proviruses are expressed in feline lymphoid cells: evidence for a role in natural resistance to subgroup B feline leukemia viruses.

Endogenous feline leukemia virus (FeLV)-related sequences (enFeLV) are a family of proviral elements found in domestic cats and their close relatives. These elements can recombine with exogenous, infectious FeLVs of subgroup A (FeLV-A), giving rise to host range variants of FeLV-B. We found that a subset of defective enFeLV proviruses is highly expressed in lymphoma cell lines and in a variety of primary tissues, including lymphoid tissues from healthy specific-pathogen-free cats. At least two RNA species were detected, a 4.5-kb RNA containing gag, env, and long terminal repeat sequences and a 2-kb RNA containing env and long terminal repeat sequences. Cloning of enFeLV cDNA from two FeLV-free lymphoma cell lines (3201 and MCC) revealed a long open reading frame (ORF) encoding a truncated env gene product corresponding to the N-terminal portion of gp70env. Interestingly, all of three natural FeLV-B isolates include 3' env sequences which are missing from the highly transcribed subset and hence must be derived from other enFeLV elements. The enFeLV env ORF cDNA clones were closely similar to a previously characterized enFeLV provirus, CFE-16, but were polymorphic at a site corresponding to an exogenous FeLV neutralization epitope. Site-specific antiserum raised to a C-terminal 30-amino-acid peptide of the enFeLV env ORF detected an intracellular product of 35 kDa which was also shed from cells in stable form. Expression of the 35-kDa protein correlated with enFeLV RNA levels and was negatively correlated with susceptibility to infection with FeLV-B. Cell culture supernatant containing the 35-kDa protein specifically blocked infection of permissive fibroblast cells with FeLV-B isolates. We suggest that the truncated env protein mediates resistance by receptor blockade and that this form of enFeLV expression mediates the natural resistance of cats to infection with FeLV-B in the absence of FeLV-A.

Animals↗

cis-acting elements in the U3 region of a simian immunodeficiency virus.

A series of 5' deletions and a point mutation in the binding site for nuclear factor kappa B were introduced into the U3 region of a molecular clone of simian immunodeficiency virus from macaques (SIVmac142). The transcriptional activity of the mutated U3 regions was analyzed by transient chloramphenicol acetyltransferase assays. Two distinct regions in U3 appeared to contain important cis-acting sequences for transcriptional activity. Mutation of the single nuclear factor kappa B site in the SIVmac142 U3 region attenuated transcription in Rat-1 fibroblasts and Jurkat T cells. A second cis-acting element was localized to sequences between -162 and -114 in U3; deletion of long terminal repeat sequences up to -114 significantly attenuated transcriptional activity in Rat-1 cells. Furthermore, sequences between -162 and -114 contributed to inducibility of transcription by 1,3-phorbol myristate acetate in Jurkat T cells. Deletion of long terminal repeat sequences to -114, in addition to mutation of the nuclear factor kappa B site, was necessary to attenuate the response to 1,3-phorbol myristate acetate completely. A negative regulatory element analogous to that identified in the U3 region from the human immunodeficiency virus was not found in the U3 region from SIVmac142.

Animals↗

Transcription in human fibroblasts permissively infected by human cytomegalovirus strain AD169.

We used cloned subgenomic DNA fragments of human cytomegalovirus strain AD169 as hybridization reagents to analyze the sites of transcription and abundance of viral RNA in permissively infected human embryonic lung cells. RNA extracted from immediate early, early, middle, and late times in the infection was attached to filters and hybridized with excess cloned subgenomic fragments. Each hybridization was performed with an internal standard to allow quantitation of the RNA concentration and standardization for the variation in probe complexity and specific activity. We found immediate early transcription in the AD169 strain occurring primarily from three regions in the long unique segment at 0.061-0.110, 0.117-0.142, and 0.588-0.616 map units. A low level of transcription was also detected from the long unique segment at 0.230-0.372, 0.419-0.437 and 0.703-0.707 map units and the short unique segment and terminal repeats at 0.00-0.046, 0.776-0.854, and 0.892-1.00 map units. At 8 hr after infection in the presence of de novo protein synthesis, the transcription pattern was changed. Two of the major immediate early sites at 0.061-0.110 and 0.117-0.142 map units were represented less abundantly in the absence of cycloheximide while the site at 0.588-0.616 map units was represented at the same level. The most abundant early RNA was synthesized from the terminal repeat sequences and part of the short unique segment at 0.00-0.046, 0.776-0.822, and 0.892-1.00 map units. Steady-state RNA from the midpoint of the infection hybridized with most regions of the genome. Abundantly transcribed regions included the abundant early sites mentioned above (0.00-0.046, 0.588-0.616, 0.776-0.822, and 0.892-1.00 map units), several new sites in the long unique segment at 0.104-0.110, 0.576-0.588, 0.653-0.664, 0.703-0.707, and 0.766-0.776 map units and the L-S junction fragment at 0.804-0.854 map unit. RNA from late in the infection hybridized to all subgenomic fragments. The sites of de novo RNA synthesis along the genome were determined by hybridizing pulse-labeled RNA to individual cloned subgenomic fragments attached to filters. Transcription from the terminal repeat sequences and the long unique segment at 0.576-0.588 map unit accounted for 40% of the total viral RNA synthesized from 22 to 28 hr after infection. Of the total de novo RNA synthesis from 71 to 77 hr after infection, 4.3% was virus specific and 47% of the total de novo synthesized viral RNA hybridized to the terminal repeat sequences.

Cell Line↗

Involvement of long terminal repeat U3 sequences overlapping the transcription control region in human immunodeficiency virus type 1 mRNA 3' end formation.

In retroviral proviruses, the poly(A) site is present in both long terminal repeats (LTRs) but used only in the 3' position. One mechanism to account for this selective poly(A) site usage is that LTR U3 sequences, transcribed only from the 3' poly(A) site, are required in the RNA for efficient processing. To test this possibility, mutations were made in the human immunodeficiency virus type 1 (HIV-1) U3 region and the mutated LTRs were inserted into simple and complex transcription units. HIV-1 poly(A) site usage was then quantitated by S1 nuclease analysis following transfection of each construct into human 293 cells. The results showed that U3 sequences confined to the transcription control region were required for efficient usage of the HIV-1 poly(A) site, even when it was placed 1.5 kb from the promoter. Although the roles of U3 in processing and transcription activation were separable, optimal 3' end formation was partly dependent on HIV-1 enhancer and SP1 binding site sequences.

Cloning, Molecular↗

Epstein-Bar virus and progression of non-Hodgkin's lymphoma to Ki-1-positive, anaplastic large cell phenotype.

Epstein-Barr virus (EBV) has been implicated in the pathogenesis of a variety of lymphoproliferative disorders (LPDs) including endemic Burkitt's lymphoma, Hodgkin's disease (HD), HIV-associated non-Hodgkin's lymphomas (NHLs), and LPDs arising in immunosuppressed transplant patients. More recently, EBV has been associated with Ki-1-positive anaplastic large cell lymphoma (ALCL), a recently described NHL that shares with HD expression of the CD30 antigen Ki-1. Because EBV has been shown to induce Ki-1 expression in vitro, and ALCL has been diagnosed in patients with prior or concurrent HD or NHL, it has been proposed that EBV may mediate progression of a "primary" lymphoma to a "secondary" ALCL. We report a case in which an AIDS-associated, Ki-1-negative, large-cell immunoblastic lymphoma progressed to a Ki-1 positive ALCL. Analysis of the immunoglobulin heavy chain locus revealed a clonal relationship between these morphologically and immunophenotypically distinct tumors. Although EBV was absent from the original large-cell immunoblastic lymphoma as assessed by in situ hybridization for EBV-encoded small RNA1 (EBER1), polymerase chain reaction for EBNA-1, immunocytochemistry for latent membrane protein 1, and Southern blot hybridization for EBV terminal repeat sequences, all for techniques confirmed the presence of EBV in the secondary ALCL. Moreover, analysis of EBV terminal repeat sequences indicated that the ALCL resulted from expansion of a single EBV-infected clone. These data suggest that EBV may mediate progression of NHL to Ki-1-positive ALCL, and that in some instances, EBV may be involved in the later stages of clonal progression of NHL.

AIDS-Related Opportunistic Infections↗

Functional and defective components of avian endogenous virus long terminal repeat enhancer sequences.

Oncogenic avian retroviruses, such as Rous sarcoma virus (RSV) and the avian leukosis viruses, contain a strong enhancer in the U3 portion of the proviral long terminal repeat (LTR). The LTRs of a second class of avian retroviruses, the endogenous viruses (ev) lack detectable enhancer activity. By creating ev-RSV hybrid LTRs, we previously demonstrated that, despite the lack of independent enhancer activity in the ev U3 region, ev LTRs contain sequences that are able to functionally replace essential enhancer domains from the RSV enhancer. A hypothesis proposed to explain these data was that ev LTRs contain a partial enhancer that includes sequences necessary but not sufficient for enhancer activity and that these sequences were complemented by RSV enhancer domains present in the original hybrid constructs to generate a functional enhancer. Studies described in this report were designed to define sequences from both the ev and RSV LTRs required to generate this composite enhancer. This was approached by generating additional ev-RSV hybrid LTRs that exchanged defined regions between ev and RSV and by directly testing the requirement for specific motifs by site-directed mutagenesis. Results obtained demonstrate that ev enhancer sequences are present in the same relative location as upstream enhancer sequences from RSV, with which they share limited sequence similarity. In addition, a 67-bp region from the internal portion of the RSV LTR that is required to complement ev enhancer sequences was identified. Finally, data showing that CArG motifs are essential for high-level activity, a finding that has not been previously demonstrated for retroviral LTRs, are presented.

Avian Leukosis Virus↗

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

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

Animals↗

Nucleotide sequences of integrated Moloney sarcoma provirus long terminal repeats and their host and viral junctions.

Integrated Moloney murine sarcoma provirus (MSV) has direct terminal repeat sequences (TRS). We determined the nucleotide sequence of both 588-base-pair TRS elements and the adjacent host and viral junctions of an integrated MSV cloned in bacteriophage lambda. Sequences were identified corresponding to the tRNAPro primer binding site in genomic RNA and the reverse-transcribed minus strong stop DNA. Each 588-base-pair repeat contains putative sites for promoting RNA synthesis and RNA polyadenylylation. The first and last 11 nucleotides of the TRS are inverted with respect to each other, and the same four-nucleotide host sequence is found bracketing integrated MSV. Some similarities of TRS and prokaryotic insertion sequence elements are discussed.

Animals↗

Long terminal repeat (LTR) sequences, env, and a region near the 5' LTR influence the pathogenic potential of recombinants between Rous-associated virus types 0 and 1.

A series of recombinants between Rous-associated virus type 0 (RAV-0), RAV-1, and a replication-competent avian leukosis virus vector (RCAN) have been tested for disease potential in day-old inoculated K28 chicks. RAV-0 is a benign virus, whereas RAV-1 and RCAN induce lymphoma and a low incidence of a variety of other neoplasms. The results of the oncogenicity tests indicate that (i) the long terminal repeat regions of RAV-1 and RCAN play a major role in disease potential, (ii) subgroup A envelope glycoproteins are associated with a two- to fourfold higher incidence of lymphoma than subgroup E glycoproteins, and (iii) certain combinations of 5' viral and env sequences cause osteopetrosis in a highly context-dependent manner. Long terminal repeat and env sequences appeared to influence lymphomogenic potential by determining the extent of bursal infection within the first 2 to 3 weeks of life. This would suggest that bursal but not postbursal stem cells are targets for avian leukosis virus-induced lymphomogenesis. The induction of neutralizing antibody had no obvious influence on the incidence of lymphoma.

Animals↗

Unregulated expression of the erythropoietin receptor gene caused by insertion of spleen focus-forming virus long terminal repeat in a murine erythroleukemia cell line.

A murine erythroleukemia (MEL) cell line, F5-5, expressed 10,000 binding sites for erythropoietin (EPO) per cell, 10-fold more than was expressed by other murine erythroleukemia cell lines and normal erythroid progenitors. Northern (RNA) and Southern blot analyses revealed overexpression of mRNA for the EPO receptor (EPOR) and rearrangement of one of the EPOR gene alleles in F5-5 cells, respectively. Molecular cloning of F5-5-derived cDNA encoding EPOR revealed that the 5' noncoding region of the EPOR cDNA corresponds to the 3' long terminal repeat sequence of the polycythemic strain of Friend spleen focus-forming virus (F-SFFVP). The aberrant EPOR transcripts containing the 3' long terminal repeat sequence were mainly expressed in F5-5 cells. The same integration upstream of the EPOR gene was also observed in other subclones and the parent cell line. It is possible that overexpression of EPOR by viral promoter insertion will confer growth advantage to an F-SFFVP-infected erythroid progenitor cell, leading to positive clonal selection through further leukemogenic steps.

Amino Acid Sequence↗

Mariner (Mos1) transposase and genomic integration of foreign gene sequences in Bombyx mori cells.

Widespread occurrence in insects and the capacity to transpose in the absence of host-derived factors means that mariner-like elements are considered to be attractive candidates for the development of a universal insect genetic transformation system. Here we show that the Mos1 mariner element of Drosophila mauritiana is capable of mediating excision and transposition events in a silkmoth (Bombyx mori) derived tissue culture cell line (Bm5 cells). Plasmid rescue assays, in combination with Southern hybridization and polymerase chain reaction (PCR) analyses, confirm that the Mos1 transposase can mediate excision of DNA sequences, inserted between terminally repeated sequences recognized by the transposase, and integration into the chromosomal DNA of the Bm5 cells. In addition to chromosomal integration events, inter- and intraplasmid transposition and target element excision events were also detected. Approximately 50% of the plasmids recovered from plasmid rescue assays were found to contain the 'signature' of Mos1-specific excision and/or integration events, indicating that the mariner transposase functions efficiently in the Bombyx cells. Because mariner-induced excision and integration events are strictly dependent on the presence of a co-transfected Mos1 transposase expression vector, it is clear that the multiple copies of endogenous mariner-like elements (Bmmar1) that exist in the Bombyx genome are neither functional nor do they interfere with the efficiency of the transposition process. Thus, the Mos1 element and, probably, mariner elements, in general, hold great promise for the development of genetic transformation systems for lepidopteran insects.

Animals↗

Differentiation between two distinct classes of viruses now classified as human herpesvirus 6.

Human herpesvirus 6 (HHV-6) causes exanthem subitum (ES, roseola infantum), a childhood disease characterized by high fever and skin rash. We have analyzed restriction enzyme cleavage patterns of the DNAs of ES virus isolates from Japan and the United States. The patterns of all the ES viral DNAs were highly conserved, except for variable sequences within the terminal repeat sequences. They resembled closely the restriction enzyme patterns of the Z29 strain of HHV-6 but were distinct from those of the U1102 strain. That all ES isolates were closely related whereas the U1102 patterns were very different suggests that the U1102 strain represents a distinct virus. Moreover, the ES isolates all resembled the Z29 strain and not the U1102 strain with respect to reactivity with HHV-6 monoclonal antibodies. These findings provide evidence for the existence of two distinct classes of viruses previously classified as HHV-6. Whereas the Z29-like viruses are involved in ES infections, the association of the U1102-like viruses with human disease has yet to be determined.

Antigens, Viral↗

Repetitive DNA and chromosome evolution in plants.

Most higher plant genomes contain a high proportion of repeated sequences. Thus repetitive DNA is a major contributor to plant chromosome structure. The variation in total DNA content between species is due mostly to variation in repeated DNA content. Some repeats of the same family are arranged in tandem arrays, at the sites of heterochromatin. Examples from the Secale genus are described. Arrays of the same sequence are often present at many chromosomal sites. Heterochromatin often contains arrays of several unrelated sequences. The evolution of such arrays in populations is discussed. Other repeats are dispersed at many locations in the chromosomes. Many are likely to be or have evolved from transposable elements. The structures of some plant transposable elements, in particular the sequences of the terminal inverted repeats, are described. Some elements in soybean, antirrhinum and maize have the same inverted terminal repeat sequences. Other elements of maize and wheat share terminal homology with elements from yeast, Drosophila, man and mouse. The evolution of transposable elements in plant populations is discussed. The amplification, deletion and transposition of different repeated DNA sequences and the spread of the mutations in populations produces a turnover of repetitive DNA during evolution. This turnover process and the molecular mechanisms involved are discussed and shown to be responsible for divergence of chromosome structure between species. Turnover of repeated genes also occurs. The molecular processes affecting repeats imply that the older a repetitive DNA family the more likely it is to exist in different forms and in many locations within a species. Examples to support this hypothesis are provided from the Secale genus.

Animals↗

New type of starch-binding domain: the direct repeat motif in the C-terminal region of Bacillus sp. no. 195 alpha-amylase contributes to starch binding and raw starch degrading.

The alpha-amylase from Bacillus sp. no. 195 (BAA) consists of two domains: one is the catalytic domain similar to alpha-amylases from animals and Streptomyces in the N-terminal region; the other is the functionally unknown domain composed of an approx. 90-residue direct repeat in the C-terminal region. The gene coding for BAA was expressed in Streptomyces lividans TK24. Three active forms of the gene products were found. The pH and thermal profiles of BAAs, and their catalytic activities for p-nitrophenyl maltopentaoside and soluble starch, showed almost the same behaviours. The largest, 69 kDa, form (BAA-alpha) was of the same molecular mass as that of the mature protein estimated from the nucleotide sequence, and had raw-starch-binding and -degrading abilities. The second largest, 60 kDa, form (BAA-beta), whose molecular mass was the same as that of the natural enzyme from Bacillus sp. no. 195, was generated by proteolytic processing between the two repeat sequences in the C-terminal region, and had lower activities for raw starch binding and degrading than those of BAA-alpha. The smallest, 50 kDa, form (BAA-gamma) contained only the N-terminal catalytic domain as a result of removal of the C-terminal repeat sequence, which led to loss of binding and degradation of insoluble starches. Thus the starch adsorption capacity and raw-starch-degrading activity of BAAs depends on the existence of the repeat sequence in the C-terminal region. BAA-alpha was specifically adsorbed on starch or dextran (alpha-1,4 or alpha-1,6 glucan), and specifically desorbed with maltose or beta-cyclodextrin. These observations indicated that the repeat sequence of the enzyme was functional in the starch-binding domain (SBD). We propose the designation of the homologues to the SBD of glucoamylase from Aspergillus niger as family I SBDs, the homologues to that of glucoamylase from Rhizopus oryzae as family II, and the homologues of this repeat sequence of BAA as family III.

Adsorption↗

Structure of the baboon endogenous virus genome: nucleotide sequences of the long terminal repeat.

The entire nucleotide sequence of the long terminal repeat (LTR) of baboon endogenous virus (BaEV) M7 was determined, which consisted of 554 base pairs (bp). At both ends of the LTR, 13 bp sequences, AAATGAAAAGTAA and TGATTCTAACATC, were detected to be inverted repeats. The structure with these inverted repeats resembles those of other retroviruses and transposable elements. a Hogness box, TATAAAA, and a putative poly(A)-addition signal, AGTAAA, were present within the right-hand half of the LTR, where the initiation and termination of the viral RNA synthesis seems to occur in the integrated BaEV genome. The primer-binding site of at least 14 bp long was found just outside of the LTR where the strong stop DNA started, and the primer for reverse transcription in BaEV seemed to be tRNAPro. Several structural features are commonly detected in the LTRs of BaEV and other retroviruses. Our studies suggest that BaEV has evolved from a common ancestor with other mammalian type C viruses. Close relationships between BaEV and a feline endogenous virus, RD114, are demonstrated.

Cloning, Molecular↗

Analysis of the terminal repeat binding abilities of mutant adeno-associated virus replication proteins.

The adeno-associated virus (AAV) Rep78 and Rep68 proteins play essential roles in viral DNA replication, trans activation of viral gene expression, and suppression of oncogene-mediated cellular transformation. By using an extensive set of linker insertion and deletion mutations in the replication gene, we mapped the regions of the Rep78 protein that mediate binding to the AAV origin of replication in vitro. Deletions that removed amino acid codons 25 to 62, 88 to 113, 125 to 256, and 346 to 400 abolished binding. Alterations in several other regions of the protein affected the binding affinity of the mutant proteins. All of the mutant proteins that support AAV DNA replication or p40 trans activation bound to the terminal repeat sequence, thus verifying the importance of binding for these functions. Several mutant rep genes that failed to suppress oncogene-mediated cellular transformation produced proteins that were capable of binding to the AAV terminal repeat sequences.

DNA Mutational Analysis↗

Stronger anti-HIV-1 activity of C-peptide derived from HIV-1 89.6 gp41 C-terminal heptad repeated sequence.

C34-LAI containing amino acids 118 to 151 of the HIV-1(LAI) gp41 ectodomain exhibits potent anti-HIV-1 activity. However, the N-terminal halves of C34 peptides vary more according to the HIV-1 strain than the C-terminal halves. Therefore, an analysis was conducted on the anti-HIV-1 activities of the C34 peptides derived from various HIV-1 strains. C34-89.6 exhibited the strongest anti-HIV-1 activity among the C34 peptides tested. Interestingly, its N-terminal half was more acidic than those of the other C34 peptides, whereas its C-terminal half was more basic. Since the C-peptides derived from the HIV-1(LAI) strain are used extensively, the anti-HIV-1 activities of these peptides were compared between the HIV-1 strains 89.6 and LAI. When using chimeric peptides, it was found that the C-terminal basic region of C34-89.6 was more critical than its N-terminal basic region. The anti-HIV-1 activity of T20-89.6 and C28-89.6 was also stronger than that of T20-LAI and C28-LAI, respectively. The anti-HIV-1 activity of C28-89.6 was weakened when the C-terminal basic residues were changed to the corresponding residues of C28-LAI. However, no conformational differences were found among the C28 peptides. Accordingly, these results imply that introducing the C-terminal basic residues of the HIV-1 89.6 C-peptide may be useful for developing potent anti-HIV-1 drugs.

Amino Acid Sequence↗

Myb protein binds to human immunodeficiency virus 1 long terminal repeat (LTR) sequences and transactivates LTR-mediated transcription.

The protooncogene c-myb encodes a nuclear transcription factor that binds to DNA in a sequence-specific manner and transactivates transcription of several viral and cellular genes. The expression of c-myb is induced in mitogen-stimulated peripheral blood lymphocytes and is constitutively expressed in several CD4+ T-cell and myeloid cell lines, all of which constitute excellent targets for human immunodeficiency virus (HIV) infection and replication. We looked for the presence of Myb-binding motifs in human retroviral long terminal repeats (LTRs) and tested for Myb binding to HIV-1 LTR sequences by using a highly purified recombinant Myb protein. Our results show that HIV-1 LTR contains one high-affinity Myb-binding site along with two or more low-affinity binding sites. DNase I protection analysis as well as oligonucleotide competition experiments indicate that this binding is sequence specific. Introduction of purified Myb protein directly into HeLa cells harboring HIV-1 LTR chloramphenicol acetyltransferase vectors indicates that Myb protein transactivates HIV-1 LTR-mediated transcription. Thus, Myb protein binding to HIV LTR sequences may constitute one of the signals that regulates HIV-1 transcription.

Base Sequence↗