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J Nicholas

Publications and source records attributed to J Nicholas.

12 recordsLinked to original sources
PubMed1992

Herpesvirus saimiri encodes homologues of G protein-coupled receptors and cyclins.

Herpesvirus saimiri (HVS) is a T-lymphotropic gammaherpesvirus which establishes asymptomatic infections in its natural host the squirrel monkey (Saimiri sciureus), but which causes fatal lymphoproliferative diseases in other New World primates. Sequencing studies show HVS is closely related to the human B-lymphotropic gammaherpesvirus Epstein-Barr virus (EBV). However, despite the general colinearity between the genomes of HVS and EBV, HVS contains genes not found in EBV or in the genomes of any of the other sequenced herpesviruses. We have identified two genes, occurring in a region of divergence between HVS and EBV, that have cellular homologues. One of these, ECRF3, is homologous to the genes encoding the human cytomegalovirus (HCMV) and cellular G protein-coupled receptor family of proteins. The other HVS gene, ECLF2, is homologous to the genes encoding cellular cyclins and to our knowledge is the first reported example of a viral cyclin. The presence of G protein-coupled receptor and cyclin homologues in HVS suggests that these genes may be important in the regulation of viral and cellular processes during productive and/or latent infection of host cells, and in particular may be of relevance in the transformation and rapid proliferation of T cells during HVS infections of hosts susceptible to HVS-induced lymphoproliferative diseases.

Amino Acid Sequence↗
PubMed1992

Analysis of nucleotide sequence of the rightmost 43 kbp of herpesvirus saimiri (HVS) L-DNA: general conservation of genetic organization between HVS and Epstein-Barr virus.

We present an analysis of 43,658 bp of contiguous nucleotide sequence comprising the right terminal region (conventional orientation) of the unique protein-coding component (L-DNA) of the herpesvirus saimiri (HVS) genome. Within this region lie the genes encoding the 160-kDa virion protein, which is homologous to the 140-kDa membrane antigen of Epstein-Barr virus (EBV), thymidylate synthase (TS), and the immediate-early (IE) 52-kDa protein which is homologous to the EBV BMLF1 product. The 160-kDa gene of HVS lies at the right terminus of HVS L-DNA, its homologue in EBV occurring at the left terminus of the EBV genome (conventional orientation). The TS gene of HVS occurs within a group of 5 genes that have no homologues in EBV. The translation product of one of these genes, ECRF3, shows amino acid sequence and hydrophobicity pattern similarities to the HCMV and cellular G-protein-coupled receptor family of proteins. Another, ECLF2, is homologous to the cyclin family of cellular proteins. The 5 nonconserved genes lie adjacent to the 160-kDa gene. In EBV, the region to the right of the 140-kDa gene (BNRF1) contains the latent replication origin (OriP) and the open reading frames BCRF1, BWRF1 (repeated 12 times), BYRF1, BHLF1, and BHRF1, counterparts of which are not present in this position in HVS. The subsequent 18 genes in EBV (BFLF2 to BLRF2, approximate positions 56,000-89,500) are represented in HVS, and the relative positions and orientations of these genes are directly comparable between the two viruses. There then occurs a nonhomologous gene in HVS, and genes BLLF2 to BZLF1 (positions 89,500 to 103,200) in EBV which are not present in this region of HVS, before collinearity resumes. Thus, the HVS sequence presented here shows general collinearity between conserved genes in the right terminal region of HVS and the left terminal region of EBV and reveals the presence of two sets of unique genes which occur in exactly analogous positions in HVS and EBV.

Amino Acid Sequence↗
PubMed1992

Genetic relationships between bovine herpesvirus 4 and the gammaherpesviruses Epstein-Barr virus and herpesvirus saimiri.

The overall arrangement of genes in the unique central part of the bovine herpesvirus type 4 (BHV-4) genome has been deduced by analysis of short DNA sequences. Twenty-three genes conserved in at least one of the completely sequenced herpesviruses have been identified and localized. All of these genes encoded amino acid sequences with higher similarity to proteins of the gammaherpesviruses Epstein-Barr virus (EBV) and herpesvirus saimiri (HVS) than to the homologous products of the alphaherpesviruses varicella-zoster virus and herpes simplex virus type 1 or the betaherpesvirus human cytomegalovirus. The genome organization of BHV-4 had also an overall colinearity with that of the gammaherpesviruses EBV and HVS. Furthermore, the BHV-4 genes content and arrangement were more similar to those of HVS than to those of EBV, suggesting that BHV-4 and HVS are evolutionarily more closely related to each other than either are to EBV. BHV-4 DNA sequences were generally deficient in CpG dinucleotide. This CpG deficiency is characteristic of gammaherpesvirus genomes and suggests that the BHV-4 latent genome is extensively methylated. Despite several biological features similar to those of betaherpesviruses, BHV-4 displays the molecular characteristics of the representative members of the gammaherpesvirinae subfamily.

Amino Acid Sequence↗
PubMed1992

Herpesvirus saimiri has a gene specifying a homologue of the cellular membrane glycoprotein CD59.

Herpesvirus saimiri (HSV) is a T-lymphotropic tumor virus that causes fulminant lymphomas and leukemias in various New World primates other than its natural host, the squirrel monkey (Saimiri sciureus). In the course of completing the nucleotide sequence of its genome, we identified an open reading frame of 363 nucleotides, designated HVS-15, that has no detectable homology to any other viral sequences to date. HVS-15 encodes a 121-amino-acid protein which shows significant similarities to human CD59, a phosphatidyl-inositol-glycan-anchored glycoprotein involved in T-cell activation and restriction of complement-mediated lysis. The predicted HVS-15 gene product is more similar to human CD59 than to the related murine Ly-6 antigens. A nucleotide sequence identity of 64% was found between HVS-15 and the CD59 reading frame, and a 48% identity exists between the corresponding protein sequences. The comparison of the amino acid sequences revealed a number of conserved structural features such as a similar pattern of hydrophobic termini and an identical cysteine skeleton.

Amino Acid Sequence↗
PubMed1992

Primary structure of the herpesvirus saimiri genome.

This report describes the complete nucleotide sequence of the genome of herpesvirus saimiri, the prototype of gammaherpesvirus subgroup 2 (rhadinoviruses). The unique low-G + C-content DNA region has 112,930 bp with an average base composition of 34.5% G + C and is flanked by about 35 noncoding high-G + C-content DNA repeats of 1,444 bp (70.8% G + C) in tandem orientation. We identified 76 major open reading frames and a set of seven U-RNA genes for a total of 83 potential genes. The genes are closely arranged, with only a few regions of sizable noncoding sequences. For 60 of the predicted proteins, homologous sequences are found in other herpesviruses. Genes conserved between herpesvirus saimiri and Epstein-Barr virus (gammaherpesvirus subgroup 1) show that their genomes are generally collinear, although conserved gene blocks are separated by unique genes that appear to determine the particular phenotype of these viruses. Several deduced protein sequences of herpesvirus saimiri without counterparts in most of the other sequenced herpesviruses exhibited significant homology with cellular proteins of known function. These include thymidylate synthase, dihydrofolate reductase, complement control proteins, the cell surface antigen CD59, cyclins, and G protein-coupled receptors. Searching for functional protein motifs revealed that the virus may encode a cytosine-specific methylase and a tyrosine-specific protein kinase. Several herpesvirus saimiri genes are potential candidates to cooperate with the gene for saimiri transformation-associated protein of subgroup A (STP-A) in T-lymphocyte growth stimulation.

Amino Acid Sequence↗
PubMed1992

The Epstein-Barr virus R transactivator (Rta) contains a complex, potent activation domain with properties different from those of VP16.

Rta, encoded by Epstein-Barr virus (EBV), is a potent activator of transcription via enhancer sequences located upstream of several viral genes. To identify the domains of Rta that facilitate transcription by interacting with cellular transcription factors, different segments of Rta were linked to the DNA binding domain of yeast transactivator GAL4 (residues 1 to 147). These GAL4-Rta fusion proteins were tested in transfected cells for their ability to activate the adeno E1b promoter with an upstream GAL4 DNA binding site. The acidic C-terminal domain of Rta (amino acids 520 to 605) was a potent activator but behaved differently from VP16 in dose-response and competition experiments. A subterminal domain of Rta (amino acids 416 to 519) linked to GAL4 had weak activation activity. Deletion of these domains from native Rta showed that the C-terminal domain was required for transactivation, but the subterminal domain was required only in B cells. The C-terminal activation domain of Rta contains a pattern of positionally conserved hydrophobic residues shared with VP16 and other transactivators. Substitution of several conserved hydrophobic amino acids in Rta severely impaired transactivation. The improtance of hydrophobic residues was further substantiated by comparing EBV Rta with that of herpesvirus saimiri, which revealed little sequence similarity except for a few acidic residues and the positionally conserved hydrophobic amino acids. The C-terminal domain of EBV Rta contains three partially overlapping copies of this hydrophobic motif. Mutational analysis indicated that all three copies were required for full activity. However, two of the three copies appeared to be sufficient to produce full activity on a target promoter with multiple binding sites, suggesting that these motifs are functional subdomains that can synergize.

Amino Acid Sequence↗
PubMed1991

Distinct DNA targets for trans-activation by HTLV-1 tax and adenovirus E1A.

The HTLV-1 LTR is trans-activated by both the HTLV-1 tax (p40x) and adenovirus E1A gene products. Previous experiments have localized tax-responsive cis-elements to three 21-bp repeat units within the promoter, as well as a fourth region located between the middle and proximal repeats. A sequence TGACG, resembling the ATF/CREB recognition element, is located at the center of each of these repeat units. Mutation of this ATF/CREB site in the 21-bp repeats impairs both tax and E1A-dependent trans-activation. However, assays of a variety of promoter mutants demonstrate that sequences required for E1A and tax induction differ, suggesting that these two viral trans-activators target different factors. In addition, although the adenovirus E4 promoter also contains three ATF/CREB sites involved in E1A activation, tax does not activate this promoter. Finally, we also find that the TATAA element of the HTLV-1 LTR contributes to E1A-dependent activation but not tax activation. We concluded that although both trans-activators exhibit similarities in their activation properties, the targets for activation must differ.

Adenovirus Early Proteins↗
PubMed1991

Analysis of immunity induced by the affinity-purified 21-kilodalton zygote-ookinete surface antigen of Plasmodium berghei.

By using affinity-purified ookinete surface antigen from the rodent malaria parasite Plasmodium berghei, a transmission-blocking immunity was induced in mice. Groups of mice were immunized via different routes, with total quantities of antigen ranging from 0.5 to 40 micrograms (with or without Freund adjuvant). Vaccination by the intramuscular route with 20 micrograms of antigen in the absence of adjuvant and boosted once with the same amount of protein induced a total transmission blockade. Immunoblot analysis confirmed that immune sera invariably recognized Pbs21 antigen. The isotype and titer of the anti-Pbs21 immunoglobulin G (IgG) response was determined by enzyme-linked immunosorbent assay. The antibody isotype was predominantly IgG1. The concentration of specific anti-Pbs21 IgG reached a peak of 182.45 +/- 92.13 micrograms/ml by week 7 postimmunization and fell progressively to 38 micrograms/ml at week 34 (at which time the transmission was still inhibited by 98%).

Animals↗
PubMed1991

Identification of a transactivating function mapping to the putative immediate-early locus of human herpesvirus 6.

Sequencing studies have indicated that the unique component of the human herpesvirus 6 (HHV-6) genome and the unique long segment of the human cytomegalovirus genome are genetically colinear. Of particular interest is the identification of a region of local CpG dinucleotide suppression in the genome of HHV-6, a feature conserved in the genomes of human cytomegalovirus, murine cytomegalovirus, and simian cytomegalovirus, and a characteristic of the major immediate-early loci of these viruses. Adjacent to this region in HHV-6 are approximately 30 copies of a 103- to 108-bp sequence element, which contains consensus binding sites for the transcription factors AP2 and NF kappa B, in addition to a single KpnI recognition site. Together, these KpnI repeat units may compose an immediate-early enhancer, analogous to those found in the cytomegaloviruses. We present the sequence of this region of HHV-6 and demonstrate that a transactivating function is encoded by this region. We have used polymerase chain reaction to synthesize fragments containing open reading frames and 5' sequences with or without the upstream KpnI repeat units. Effector plasmids containing these HHV-6 coding and 5' sequences were able to effect activation of heterologous promoter-chloramphenicol acetyltransferase (CAT) constructs, including adenovirus E3-CAT and E4-CAT, human T-cell lymphotropic virus type I long terminal repeat (LTR)-CAT, and human immunodeficiency virus LTR-CAT, in cotransfection experiments in Vero cells and peripheral blood lymphocytes. Furthermore, we have identified the major open reading frame (RF4; 2.3 kb) as being essential for activation, and we have shown that the NF kappa B, SP1, and TATA box motifs in the human immunodeficiency virus LTR are all required for full induction of the promoter by the HHV-6-encoded transactivator.

Amino Acid Sequence↗
PubMed1991

Regulation of the herpesvirus saimiri (HVS) delayed-early 110-kilodalton promoter by HVS immediate-early gene products and a homolog of the Epstein-Barr virus R trans activator.

We have reported previously the detection of two stable immediate-early (IE) transcripts that accumulate in cycloheximide-treated cells infected with herpesvirus saimiri (HVS). These are the 1.6-kb mRNA from the 52-kDa gene (which is homologous to the BSLF2-BMLF1 gene of Epstein-Barr virus) and the 1.3-kb mRNA from the HindIII-G fragment of virus DNA. In order to study the roles of the HVS IE gene products in the progression of a lytic infection, the promoter region of the delayed-early 110-kDa gene of HVS was sequenced, the transcription initiation site was mapped by RNase protection, and the promoter sequences were cloned upstream of the chloramphenicol acetyltransferase (CAT) gene. Sequences between -447 and +37 (relative to the 110-kDa transcription initiation site) were sufficient for response to HVS superinfection of transfected cells, but the 110-kDa promoter was activated only poorly by the 52-kDa and HindIII-G IE (IE-G) proteins in cotransfection experiments. However, a distinct region of the genome, EcoRI-D (15 kbp), was able to activate 110-kDa-CAT expression relatively efficiently in similar experiments. A 4.7-kbp PstI fragment encoding this function was isolated and sequenced, and further subcloning identified the gene encoding the EcoRI-D trans activator. This gene, which we now designate HVS.R, is homologous to the BRLF1-encoded transcriptional effector of Epstein-Barr virus.

Amino Acid Sequence↗
PubMed1990

Gene expression in cells infected with gammaherpesvirus saimiri: properties of transcripts from two immediate-early genes.

During productive infections of cells with the gammaherpesvirus, herpesvirus saimiri (HVS), a polyadenylated RNA of 2.2-2.4 kb accumulates to form a large fraction of virus-specified RNA. This transcript is from the virus thymidylate synthase (TS) gene and its synthesis, like that of late mRNAs encoding the virus structural proteins, is sensitive to an inhibitor of virus DNA synthesis (phosphonoacetic acid, PAA). Transcription which is insensitive to PAA occurs from many parts of the HVS genome, including the EcoRI-D, EcoRI-E, EcoRI-I, and HindIII-G fragments. A 1.6-kb RNA from EcoRI-I/E and a 1.3-kb RNA from HindIII-G accumulate in HVS-infected cells incubated in the continuous presence of cycloheximide, and thus represent immediate-early (IE) class transcripts. The 1.3-kb message from HindIII-G is the predominant stable RNA under these conditions; accumulation of the 1.6-kb transcript from EcoRI-I/E (which encodes the previously characterized 52-kDa IE phosphoprotein) is markedly more dependent on the multiplicity of infection. The sequence of a 2.5-kbp region of the HindIII-G fragment has been determined and a single major open reading frame is present within the boundaries of the 1.3-kb IE RNA. Comparison of the amino acid sequence of the encoded protein (IE-G) with current databases of protein sequences failed to demonstrate significant similarities with herpesvirus proteins, but did detect a significant similarity with a region of the protein specified by an open reading frame in the LTR of mouse mammary tumor virus. The function of the IE gene in HindIII-G and the basis for the distinctive multiplicity dependence of IE transcription from the 52-kDa gene remain to be established.

Amino Acid Sequence↗