101
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Verchot J, Carrington JC. Debilitation of plant potyvirus infectivity by P1 proteinase-inactivating mutations and restoration by second-site modifications. J Virol 1995; 69:1582-90. [PMID: 7853492 PMCID: PMC188753 DOI: 10.1128/jvi.69.3.1582-1590.1995] [Citation(s) in RCA: 56] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Tobacco etch virus (TEV) encodes three proteinases that catalyze processing of the genome-encoded polyprotein. The P1 proteinase originates from the N terminus of the polyprotein and catalyzes proteolysis between itself and the helper component proteinase (HC-Pro). Mutations resulting in substitution of a single amino acid, small insertions, or deletions were introduced into the P1 coding sequence of the TEV genome. Deletion of the N-terminal, nonproteolytic domain of P1 had only minor effects on virus infection in protoplasts and whole plants. Insertion mutations that did not impair proteolytic activity had no measurable effects regardless of whether the modification affected the N-terminal nonproteolytic or C-terminal proteolytic domain. In contrast, three mutations (termed S256A, F, and delta 304) that debilitated P1 proteolytic activity rendered the virus nonviable, whereas a fourth proteinase-debilitating mutation (termed C) resulted in a slow-infection phenotype. A strategy was devised to determine whether the defect in the P1 mutants was due to an inactive proteinase domain or due simply to a lack of proteolytic maturation between P1 and HC-Pro. Sequences coding for a surrogate cleavage site recognized by the TEV NIa proteinase were inserted into the genome of each processing-debilitated mutant at positions that resulted in NIa-mediated proteolysis between P1 and HC-Pro. The infectivity of each mutant was restored by these second-site modifications. These data indicate that P1 proteinase activity is not essential for viral infectivity but that separation of P1 and HC-Pro is required. The data also provide evidence that the proteinase domain is involved in additional, nonproteolytic functions.
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Affiliation(s)
- J Verchot
- Department of Biology, Texas A&M University, College Station 77843
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102
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Vance VB, Berger PH, Carrington JC, Hunt AG, Shi XM. 5' proximal potyviral sequences mediate potato virus X/potyviral synergistic disease in transgenic tobacco. Virology 1995; 206:583-90. [PMID: 7831814 DOI: 10.1016/s0042-6822(95)80075-1] [Citation(s) in RCA: 92] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The interaction of potato virus X (PVX) and potato virus Y (PVY) in tobacco causes a synergistic disease characterized by a dramatic increase in symptom severity, a change in the regulation of PVX RNA replication, and an increase in accumulation of PVX. In this study we demonstrate that PVX also interacts synergistically with three other members of the potyvirus group of plant viruses, tobacco vein mottling virus (TVMV), tobacco etch virus (TEV), and pepper mottle virus. These synergisms resemble the classic PVX/PVY synergism with respect to both the increase in host response and the change in PVX replication. To determine if the induction of PVX/potyviral synergism requires potyviral genome replication per se or if the response is mediated by expression of one or more potyviral genes, we used tobacco plants stably transformed with various subsets of the TVMV genome. PVX infections of transgenic plants expressing the 5'-proximal region of the TVMV genome, including the protease-1, helper component protease, and protein-3 genes, result in symptoms resembling those of PVX/potyviral synergism. A similar synergistic-like response occurs when transgenic tobacco plants expressing the analogous but smaller region from the 5'-proximal region of the TEV genome were infected with PVX. Replication of PVX RNA is altered in transgenic plants expressing 5'-proximal sequences of either TVMV or TEV, and in a manner similar to that observed in double infections. These results indicate that replication of the potyviral genome is not required for PVX/potyviral synergism and that the response is mediated by expression of potyviral sequences which have been localized to the 5'-proximal third of the genomic RNAs of both TVMV and TEV.
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Affiliation(s)
- V B Vance
- Department of Biological Sciences, University of South Carolina, Columbia 29208
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103
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GARCÍA JA, RIECHMANN JL, LAÍN S, MARTÍN MT, GUO H, SIMON L, FERNÁNDEZ A, DOMÍNGUEZ E, CERVERA MT. Molecular characterization of plum pox potyvirus. ACTA ACUST UNITED AC 1994. [DOI: 10.1111/j.1365-2338.1994.tb01067.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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104
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Restrepo-Hartwig MA, Carrington JC. The tobacco etch potyvirus 6-kilodalton protein is membrane associated and involved in viral replication. J Virol 1994; 68:2388-97. [PMID: 8139025 PMCID: PMC236716 DOI: 10.1128/jvi.68.4.2388-2397.1994] [Citation(s) in RCA: 103] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
The tobacco etch potyvirus (TEV) genome encodes a polyprotein that is processed by three virus-encoded proteinases. Although replication of TEV likely occurs in the cytoplasm, two replication-associated proteins, VPg-proteinase (nuclear inclusion protein a) (NIa) and RNA-dependent RNA polymerase (nuclear inclusion protein b) (NIb), accumulate in the nucleus of infected cells. The 6-kDa protein is located adjacent to the N terminus of NIa in the TEV polyprotein, and, in the context of a 6-kDa protein/NIa (6/NIa) polyprotein, impedes nuclear translocation of NIa (M. A. Restrepo-Hartwig and J. C. Carrington, J. Virol. 66:5662-5666, 1992). The 6-kDa protein and three polyproteins containing the 6-kDa protein were identified by affinity chromatography of extracts from infected plants. Two of the polyproteins contained NIa or the N-terminal VPg domain of NIa linked to the 6-kDa protein. To investigate the role of the 6-kDa protein in vivo, insertion and substitution mutagenesis was targeted to sequences coding for the 6-kDa protein and its N- and C-terminal cleavage sites. These mutations were introduced into a TEV genome engineered to express the reporter protein beta-glucuronidase (GUS), allowing quantitation of virus amplification by a fluorometric assay. Three-amino-acid insertions at each of three positions in the 6-kDa protein resulted in viruses that were nonviable in tobacco protoplasts. Disruption of the N-terminal cleavage site resulted in a virus that was approximately 10% as active as the parent, while disruption of the C-terminal processing site eliminated virus viability. The subcellular localization properties of the 6-kDa protein were investigated by fractionation and immunolocalization of 6-kDa protein/GUS (6/GUS) fusion proteins in transgenic plants. Nonfused GUS was associated with the cytosolic fraction (30,000 x g centrifugation supernatant), while 6/GUS and GUS/6 fusion proteins sedimented with the crude membrane fraction (30,000 x g centrifugation pellet). The GUS/6 fusion protein was localized to apparent membranous proliferations associated with the periphery of the nucleus. These data suggest that the 6-kDa protein is membrane associated and is necessary for virus replication.
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105
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Marcos JF, Beachy RN. In vitro characterization of a cassette to accumulate multiple proteins through synthesis of a self-processing polypeptide. PLANT MOLECULAR BIOLOGY 1994; 24:495-503. [PMID: 8123791 DOI: 10.1007/bf00024117] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
The strategy for processing the polyprotein encoded by plant potyviruses has been mimicked by constructing an expression cassette based on the nuclear inclusion (Nla) proteinase from tobacco etch virus (TEV). This cassette (pPR01), includes the TEV Nla coding region flanked on each side by its heptapeptide cleavage sequence and cloning sites for the in frame insertion of two different open reading frames. pPR01 allows the synthesis, under the control of a single transcriptional promoter, of two proteins in equimolar amounts as part of a polyprotein which is cleaved into individual mature products by the TEV protease. In in vitro reactions the cassette functioned as expected when several different protein-coding sequences were used. The potential uses of pPR01 are discussed.
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Affiliation(s)
- J F Marcos
- Department of Cell Biology, Scripps Research Institute, La Jolla, CA 92037
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106
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Yeh SD, Gonsalves D. Practices and Perspective of Control of Papaya Ringspot Virus by Cross Protection. ADVANCES IN DISEASE VECTOR RESEARCH 1994. [DOI: 10.1007/978-1-4612-2590-4_9] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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107
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Albrechtsen M, Borkhardt B. Detection of a 45 kD protein derived from the N terminus of the pea seedborne mosaic potyvirus polyprotein in vivo and in vitro. Virus Genes 1994; 8:7-13. [PMID: 8209424 DOI: 10.1007/bf01703597] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
A 45 kD protein (Pro1) derived from the N terminus of the pea seedborne mosaic potyvirus (PSbMV) polyprotein has been detected in extracts of infected pea plants and among in vitro translation products of PSbMV genomic RNA. The genomic region coding for the first 231 amino acids of the PSbMV polyprotein was cloned and expressed in Escherichia coli as a fusion protein with beta-galactosidase. A rabbit antiserum raised against the fusion protein recognized an approximately 45 kD protein in immunoblots of extracts of PSbMV-infected pea leaves that was not present in extracts of healthy leaves. The highest concentration of the 45 kD protein was found in extracts of young leaves, suggesting the protein may be rapidly degraded in vivo. After in vitro translation of PSbMV genomic RNA in a wheat germ extract, the antiserum immunoprecipitated a 45 kD polypeptide as well as some lower molecular weight translation products. On the other hand, an approximately 90 kD polypeptide was immunoprecipitated from in vitro translation products of genomic RNA in a rabbit reticulocyte lysate, corresponding to the combined molecular weights of Pro1 and the helper component predicted from genomic sequence data.
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Affiliation(s)
- M Albrechtsen
- Biotechnology Group, Danish Institute of Plant and Soil Science, Lyngby
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108
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Abstract
This chapter examines families of serine peptidases. Serine peptidases are found in viruses, bacteria, and eukaryotes. They include exopeptidases, endopeptidases, oligopeptidases, and omega peptidases. On the basis of three-dimensional structures, most of the serine peptidase families can be grouped together into about six clans that may have common ancestors. The structures are known for members of four of the clans, chymotrypsin, subtilisin, carboxypeptidase C, and Escherichia D-Ala-D-Ala peptidase A. The peptidases of chymotrypsin, subtilisin, and carboxypeptidase C clans have a common “catalytic triad” of three amino acids—namely, serine (nucleophile), aspartate (electrophile), and histidine (base). The geometric orientations of these are closely similar between families; however the protein folds are quite different. The arrangements of the catalytic residues in the linear sequences of members of the various families commonly reflect their relationships at the clan level. The members of the chymotrypsin family are almost entirely confined to animals. 10 families are included in chymotrypsin clan (SA), and all the active members of these families are endopeptidases. The order of catalytic residues in the polypeptide chain in clan SA is His/Asp/Ser.
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Affiliation(s)
- N D Rawlings
- Strangeways Research Laboratory, Cambridge, United Kingdom
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109
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Carrington JC, Haldeman R, Dolja VV, Restrepo-Hartwig MA. Internal cleavage and trans-proteolytic activities of the VPg-proteinase (NIa) of tobacco etch potyvirus in vivo. J Virol 1993; 67:6995-7000. [PMID: 8230423 PMCID: PMC238159 DOI: 10.1128/jvi.67.12.6995-7000.1993] [Citation(s) in RCA: 92] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
The NIa protein of plant potyviruses is a bifunctional protein containing an N-terminal VPg domain and a C-terminal proteinase region. The majority of tobacco etch potyvirus (TEV) NIa molecules are localized to the nucleus of infected cells, although a proportion of NIa is attached covalently as VPg to viral RNA in the cytoplasm. A suboptimal cleavage site that is recognized by the NIa proteinase is located between the two domains. This site was found to be utilized in the VPg-associated, but not the nuclear, pool of NIa. A mutation converting Glu-189 to Leu at the P1 position of the processing site inhibited internal cleavage. Introduction of this mutation into TEV-GUS, an engineered variant of TEV that expresses a reporter protein (beta-glucuronidase [GUS]) fused to the N terminus of the helper component-proteinase (HC-Pro), rendered the virus replication defective in tobacco protoplasts. Site-specific reversion of the mutant internal processing site to the wild-type sequence restored virus viability. In addition, the trans-processing activity of NIa proteinase was tested in vivo after introduction of an artificial cleavage site between the GUS and HC-Pro sequences in the cytoplasmic GUS/HC-Pro polyprotein encoded by TEV-GUS. The novel site was recognized and processed in plants infected by the engineered virus, indicating the presence of excess NIa processing capacity in the cytoplasm. The potential roles of internal NIa processing in TEV-infected cells are discussed.
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Affiliation(s)
- J C Carrington
- Department of Biology, Texas A & M University, College Station 77843
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110
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Palkovics L, Burgyán J, Balázs E. Comparative sequence analysis of four complete primary structures of plum pox virus strains. Virus Genes 1993; 7:339-47. [PMID: 8122394 DOI: 10.1007/bf01703390] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The complete nucleotide sequence of plum pox virus (PPV) strain SK 68 was determined from a series of overlapping cDNA clones. The exact 5' terminus was determined by direct RNA sequencing. The RNA sequence was 9786 nucleotides in length, excluding a 3' terminal poly(A) sequence. The large open reading frame starts at nucleotide position 147 and is terminated at position 9568. Comparison of cistrons from other plum pox virus strains with those predicted for the SK 68 strain indicated the same genomic organizations. Comparison of sequences leads to the following conclusions: (1) The genetic organization of all four PPV strains is identical, containing one large polyprotein gene and two noncoding regions at the 5' and 3' ends; (2) pairwise comparison of the genomic sequence of PPV SK 68 with other PPV strains shows 11% alteration. Sequence differences among strains are spread in a uniform manner upon the genome, except for the P1, HC-pro, and two noncoding regions, which are more conserved (with a 4% and 6.6% change). The stability of the noncoding regions is probably linked to their role in replication. The sequence variation has little effect on the amino acid sequence of the corresponding polypeptides, as changes occur preferentially in the third position of the reading frame triplets, except in the case of the 5' end of the coat protein gene (2.7% average difference in amino acid level, while in the case of coat protein it is 7.7%).(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- L Palkovics
- Institute for Plant Sciences, Agricultural Biotechnology Center, Gödöllö, Hungary
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111
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Dougherty WG, Semler BL. Expression of virus-encoded proteinases: functional and structural similarities with cellular enzymes. Microbiol Rev 1993; 57:781-822. [PMID: 8302216 PMCID: PMC372939 DOI: 10.1128/mr.57.4.781-822.1993] [Citation(s) in RCA: 198] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Many viruses express their genome, or part of their genome, initially as a polyprotein precursor that undergoes proteolytic processing. Molecular genetic analyses of viral gene expression have revealed that many of these processing events are mediated by virus-encoded proteinases. Biochemical activity studies and structural analyses of these viral enzymes reveal that they have remarkable similarities to cellular proteinases. However, the viral proteinases have evolved unique features that permit them to function in a cellular environment. In this article, the current status of plant and animal virus proteinases is described along with their role in the viral replication cycle. The reactions catalyzed by viral proteinases are not simple enzyme-substrate interactions; rather, the processing steps are highly regulated, are coordinated with other viral processes, and frequently involve the participation of other factors.
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Affiliation(s)
- W G Dougherty
- Department of Microbiology, Oregon State University, Corvallis 97331-3804
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112
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Dolja VV, Herndon KL, Pirone TP, Carrington JC. Spontaneous mutagenesis of a plant potyvirus genome after insertion of a foreign gene. J Virol 1993; 67:5968-75. [PMID: 8371351 PMCID: PMC238018 DOI: 10.1128/jvi.67.10.5968-5975.1993] [Citation(s) in RCA: 99] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
The RNA genome of tobacco etch potyvirus (TEV) was engineered to express bacterial beta-glucuronidase (GUS) fused to the virus helper component proteinase (HC-Pro). It was shown previously that prolonged periods (approximately 1 month) of TEV-GUS propagation in plants resulted in the appearance of spontaneous deletion variants. Nine deletion mutants were identified by nucleotide sequence analysis of 40 cDNA clones obtained after polymerase chain reaction amplification. The mutants were missing between 1,741 and 2,074 nucleotides from TEV-GUS, including the sequences coding for most of GUS and the N-terminal region of HC-Pro. This region of HC-Pro contains determinants involved in helper component activity during aphid transmission, as well as a highly conserved series of cysteine residues. The deletion variants were shown to replicate and move systemically without the aid of a helper virus. Infectious viruses harboring the two largest HC-Pro deletions (termed TEV-2del and TEV-7del) were reconstructed by subcloning the corresponding mutated regions into full-length DNA copies of the TEV genome. Characterization of these and additional variants derived by site-directed mutagenesis demonstrated that deletion of sequences coding for the HC-Pro N-terminal domain had a negative effect on accumulation of viral RNA and coat protein. The TEV-2del variant possessed an aphid-nontransmissible phenotype that could be rescued partially by prefeeding of aphids on active HC-Pro from another potyvirus. These data suggest that the N-terminal domain of HC-Pro or its coding sequence enhances virus replication or genome expression but does not provide an activity essential for these processes. The function of this domain, as well as a proposed deletion mechanism involving nonhomologous recombination, is discussed.
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MESH Headings
- Amino Acid Sequence
- Animals
- Aphids/microbiology
- Blotting, Northern
- Cloning, Molecular
- Cysteine/analysis
- Cysteine Endopeptidases/biosynthesis
- Cysteine Endopeptidases/genetics
- Gene Deletion
- Genes, Bacterial
- Genome, Viral
- Glucuronidase/biosynthesis
- Glucuronidase/genetics
- Immunoblotting
- Molecular Sequence Data
- Mutagenesis, Insertional
- Mutagenesis, Site-Directed
- Plant Viruses/genetics
- Plant Viruses/isolation & purification
- Plants, Toxic
- RNA, Viral/genetics
- RNA, Viral/isolation & purification
- Recombinant Fusion Proteins/biosynthesis
- Nicotiana/microbiology
- Transcription, Genetic
- Viral Proteins/biosynthesis
- Viral Proteins/genetics
- Viral Proteins/isolation & purification
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Affiliation(s)
- V V Dolja
- Department of Biology, Texas A&M University, College Station 77843-3258
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113
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Vardi E, Sela I, Edelbaum O, Livneh O, Kuznetsova L, Stram Y. Plants transformed with a cistron of a potato virus Y protease (NIa) are resistant to virus infection. Proc Natl Acad Sci U S A 1993; 90:7513-7. [PMID: 8356047 PMCID: PMC47172 DOI: 10.1073/pnas.90.16.7513] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
An oligonucleotide carrying signals for translation initiation in plants was engineered upstream to a cDNA clone containing nucleotides 5812-7260 of the potato virus Y (PVY) genome. This fragment contains all but the first 100 5' terminal bases of the cistron encoding one of the PVY proteases (NIa) as well as the first 251 bases of the next cistron (NIb). Nicotiana tabacum cv. SR1 plants were transformed with this fragment. The presence of the NIa sequences in transformed plants was determined by hybridization or PCR, and its expression was ascertained by reverse transcription coupled to PCR. Plants expressing NIa were self-pollinated, and the R1 kanamycin-resistant progeny were rechecked for NIa expression. Several of these plants were found to be resistant to PVY infection, inasmuch as they did not develop symptoms for at least 50 days (the duration of the experiments), and no viral accumulation could be detected in their leaves by ELISA. All of the descendents of resistant homozygous R2 plants were also resistant. Several of the plants transformed with the last three cistrons of PVY (bases 5812-9704; NIa-NIb-coat protein) were also resistant to PVY. None of the transformed plants exhibited resistance to tobacco mosaic virus. Exposure of the plants to 35 degrees C for 48 hr prior to inoculation lowered, but did not abolish, resistance.
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Affiliation(s)
- E Vardi
- Virus Laboratory, Hebrew University of Jerusalem, Faculty of Agriculture, Rehovot, Israel
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114
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Hijikata M, Mizushima H, Akagi T, Mori S, Kakiuchi N, Kato N, Tanaka T, Kimura K, Shimotohno K. Two distinct proteinase activities required for the processing of a putative nonstructural precursor protein of hepatitis C virus. J Virol 1993; 67:4665-75. [PMID: 8392606 PMCID: PMC237852 DOI: 10.1128/jvi.67.8.4665-4675.1993] [Citation(s) in RCA: 375] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Gene products of hepatitis C virus (HCV), a possible major causative agent of posttransfusion non-A, non-B hepatitis, are considered to be produced from a precursor polyprotein via proteolytic processing mediated by either host cell or viral proteinases. The presence of HCV serine proteinase has been proposed from analyses of amino acid sequence homology. To examine the processing mechanism of the HCV precursor polyprotein, the amino-terminal region of the putative nonstructural protein region of the HCV genome, containing the serine proteinase motif, was expressed and analyzed by using an in vitro transcription/translation system and a transient expression system in cultured cells. Two distinct proteinase activities which function in the production of a 70-kDa protein (p70) from the precursor polyprotein were detected. One of these proteinase activities, which cleaved the carboxyl (C)-terminal side of p70, required the presence of the serine proteinase motif, which is located in the amino (N)-terminal region of p70. That suggested that the predicted HCV serine proteinase was functional. The other activity, which was responsible for the cleavage of the N-terminal side of p70, required the expression of the region upstream and downstream of that cleavage site, including the p70 serine proteinase domain. From the results of pulse-chase analysis, using proteinase inhibitors coupled with a point mutation analysis, the latter activity was proposed to be a novel zinc-dependent metalloproteinase.
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Affiliation(s)
- M Hijikata
- Virology Division, National Cancer Center Research Institute, Tokyo, Japan
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115
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García JA, Cervera MT, Riechmann JL, López-Otín C. Inhibitory effects of human cystatin C on plum pox potyvirus proteases. PLANT MOLECULAR BIOLOGY 1993; 22:697-701. [PMID: 8343605 PMCID: PMC7089253 DOI: 10.1007/bf00047410] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/15/1992] [Accepted: 03/24/1993] [Indexed: 05/22/2023]
Abstract
The effect of different protease inhibitors on the proteolytic processing of the plum pox potyvirus (PPV) polyprotein has been analyzed. Human cystatin C, an inhibitor of cysteine proteases, interfered with the autoprocessing of the viral papain-like cysteine protease HCPro. Unexpectedly, it also had an inhibitory effect on the autocatalytic cleavage of the Nla protease which, although it has a Cys residue in its active center, has been described as structurally related to serine proteases. Other protease inhibitors tested had no effect on any of the cleavage events analyzed.
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Affiliation(s)
- J A García
- Centro de Biología Molecular (CSIC-UAM)-Centro Nacional de Biotecnología, Campus de la Universidad Autónoma de Madrid, Spain
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116
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Stram Y, Chetsrony A, Karchi H, Karchi M, Edelbaum O, Vardi E, Livneh O, Sela I. Expression of the "helper component" protein of potato virus Y (PVY) in E. coli: possible involvement of a third protease. Virus Genes 1993; 7:151-6. [PMID: 8367942 DOI: 10.1007/bf01702395] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Transmission of potyviruses by aphids depends on the presence of a virus encoded helper-component protein (HC) that also exhibits protease activity. HC was expressed in E. coli from two types of clones: a full-length cDNA clone of PVY and two 5' end clones containing the first three cistrons (3.6-3.7 kbp). The clones derived from the 5' end of PVY expressed HC of the size of the mature component. Other proteins reacting with antibodies to HC were also observed, and their sizes corresponded with those of expected intermediates resulting from partial protease cleavage of the three-cistron polyprotein. On the other hand, the only detectable HC-related product of the full-length clone was a mature-size HC. The presence of a third PVY protease among the first three cistrons is therefore suggested.
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Affiliation(s)
- Y Stram
- Virus Laboratory, Hebrew University of Jerusalem, Faculty of Agriculture, Rehovot, Israel
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117
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Stram Y, Sela I, Edelbaum O, Tanne E, Karchi M, Karchi H. Expression and assembly of the potato virus Y (PVY) coat protein (CP) in Escherichia coli cells. Virus Res 1993; 28:29-35. [PMID: 8493811 DOI: 10.1016/0168-1702(93)90087-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
A clone harboring the full-length cDNA of potato virus Y in a lambda-DASH vector under the control of a T7 promoter was introduced into Escherichia coli carrying the T7-RNA-polymerase gene on a plasmid. The viral coat protein was expressed and the product was of the same size as the corresponding mature protein in infected plants. Immunoelectronmicroscopy of transfected cell extracts revealed virus-like particles, indicating that the proteins involved in its processing and the viral coat protein retained their native activity.
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Affiliation(s)
- Y Stram
- Virus Laboratory, Hebrew University of Jerusalem, Faculty of Agriculture, Rehovot, Israel
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118
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Thole V, Dalmay T, Burgyán J, Balázs E. Cloning and sequencing of potato virus Y (Hungarian isolate) genomic RNA. Gene 1993; 123:149-56. [PMID: 8428653 DOI: 10.1016/0378-1119(93)90118-m] [Citation(s) in RCA: 73] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
A sequence of 9703 nucleotides (nt) is reported for the genomic RNA of potato virus Y (Hungarian isolate, PVY-H), which causes necrotic rings around the buds on the tubers and mottling of leaves. The sequence contains one large open reading frame of 3061 amino acids (aa), a noncoding region of 189 nt at the 5' end and a 330-nt 3' nontranslated region. The nt sequence and the predicted aa sequence of the polyprotein of PVY-H were analysed pairwise with the only available complete sequence of PVY strain N (PVYn) and with the partial sequences of different PVY strains, as well as with other potyviruses and potyvirus-related plant viruses. The overall relationship between PVY-H and PVYn shows a nt sequence identity of 88.5% and an aa sequence identity of 94.2%. The lowest degree of homology was detected at the 5' terminus of the genome, including the 5' noncoding region (70.3%) and the 275-aa P1 protein (78%). A fivefold sequence repeat block of 5'-UUUCA was found in the 5' noncoding region of PVY-H, which seems to be characteristic of PVY strains.
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Affiliation(s)
- V Thole
- Agricultural Biotechnology Center, Institute for Plant Sciences, Gödöllö, Hungary
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119
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Ravelonandro M, Peyruchaud O, Garrigue L, de Marcillac G, Dunez J. Immunodetection of the plum pox virus helper component in infected plants and expression of its gene in transgenic plants. Arch Virol 1993; 130:251-68. [PMID: 8517789 DOI: 10.1007/bf01309658] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/1992] [Accepted: 12/15/1992] [Indexed: 01/31/2023]
Abstract
Tobacco plants (Nicotiana tabacum cv. Xanthi) have been transformed via Agrobacterium tumefaciens vectors, with cDNAs corresponding to the plum pox virus (PPV) cistron 2 encoding helper component (HC-Pro) and with the first two and half cistrons of the PPV genome. Presence of the HC-Pro in PPV-infected plants and transgenic plants transformed with the gene coding for this protein was investigated using specific polyclonal antibodies produced against the PPV HC-Pro. The results suggest that two proteases are involved in the processing of the PPV N-terminal polyprotein to yield a protein of 48 k (HC-Pro). HC-Pro autolytically cleaves at its carboxyl-terminus and a proteolytic activity, probably associated with the protein (P1) encoded by the cistron 1, is required for the cleavage in planta between the proteins derived from cistrons 1 and 2.
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Affiliation(s)
- M Ravelonandro
- INRA, Centre de Recherches de Bordeaux, Villenave d'Ornon, France
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120
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Koonin EV, Dolja VV. Evolution and taxonomy of positive-strand RNA viruses: implications of comparative analysis of amino acid sequences. Crit Rev Biochem Mol Biol 1993; 28:375-430. [PMID: 8269709 DOI: 10.3109/10409239309078440] [Citation(s) in RCA: 714] [Impact Index Per Article: 23.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Despite the rapid mutational change that is typical of positive-strand RNA viruses, enzymes mediating the replication and expression of virus genomes contain arrays of conserved sequence motifs. Proteins with such motifs include RNA-dependent RNA polymerase, putative RNA helicase, chymotrypsin-like and papain-like proteases, and methyltransferases. The genes for these proteins form partially conserved modules in large subsets of viruses. A concept of the virus genome as a relatively evolutionarily stable "core" of housekeeping genes accompanied by a much more flexible "shell" consisting mostly of genes coding for virion components and various accessory proteins is discussed. Shuffling of the "shell" genes including genome reorganization and recombination between remote groups of viruses is considered to be one of the major factors of virus evolution. Multiple alignments for the conserved viral proteins were constructed and used to generate the respective phylogenetic trees. Based primarily on the tentative phylogeny for the RNA-dependent RNA polymerase, which is the only universally conserved protein of positive-strand RNA viruses, three large classes of viruses, each consisting of distinct smaller divisions, were delineated. A strong correlation was observed between this grouping and the tentative phylogenies for the other conserved proteins as well as the arrangement of genes encoding these proteins in the virus genome. A comparable correlation with the polymerase phylogeny was not found for genes encoding virion components or for genome expression strategies. It is surmised that several types of arrangement of the "shell" genes as well as basic mechanisms of expression could have evolved independently in different evolutionary lineages. The grouping revealed by phylogenetic analysis may provide the basis for revision of virus classification, and phylogenetic taxonomy of positive-strand RNA viruses is outlined. Some of the phylogenetically derived divisions of positive-strand RNA viruses also include double-stranded RNA viruses, indicating that in certain cases the type of genome nucleic acid may not be a reliable taxonomic criterion for viruses. Hypothetical evolutionary scenarios for positive-strand RNA viruses are proposed. It is hypothesized that all positive-strand RNA viruses and some related double-stranded RNA viruses could have evolved from a common ancestor virus that contained genes for RNA-dependent RNA polymerase, a chymotrypsin-related protease that also functioned as the capsid protein, and possibly an RNA helicase.
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Affiliation(s)
- E V Koonin
- National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD 20894
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121
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Vance VB, Moore D, Turpen TH, Bracker A, Hollowell VC. The complete nucleotide sequence of pepper mottle virus genomic RNA: comparison of the encoded polyprotein with those of other sequenced potyviruses. Virology 1992; 191:19-30. [PMID: 1413501 DOI: 10.1016/0042-6822(92)90162-i] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The complete nucleotide sequence of a pepper mottle virus isolate from California (PepMoV C) has been determined from cloned viral cDNAs. The PepMoV C genomic RNA is 9640 nucleotides excluding the poly(A) tail and contains a long open reading frame starting at nucleotide 168 and potentially encoding a polyprotein of 3068 amino acids. Comparison of the PepMoV C presumptive polyprotein with those of other sequenced members of the potyvirus group, including tobacco etch virus (TEV), tobacco vein mottling virus (TVMV), plum pox virus (PPV), and potato virus Y (PVY), allowed localization of putative protein cleavage sites. A similar analysis was used to determine the position of conserved viral protein-coding regions along the viral genomic RNA. These analyses confirm previous work indicating that genome organization is conserved among members of the genus Potyvirus. The localization of one PepMoV C gene product, the nuclear inclusion body protein a (NIa protein), was analyzed by expressing PepMoV cDNA deletion clones in bacteria and assaying for appearance of mature-sized coat protein, a cleavage product of the NIa protease. Comparative sequence analyses of the putative PepMoV polyprotein with those of TEV, TVMV, PPV, and PVY served to identify regions of the potyviral polyproteins which have diverged within the genus, as well as highly conserved protein features which may play an important functional role in the potyviral life cycle.
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Affiliation(s)
- V B Vance
- Department of Biological Sciences, University of South Carolina, Columbia 29208
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122
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Ravelonandro M, Monsion M, Teycheney PY, Delbos R, Dunez J. Construction of a chimeric viral gene expressing plum pox virus coat protein. Gene 1992; 120:167-73. [PMID: 1398133 DOI: 10.1016/0378-1119(92)90090-c] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The capsid-encoding gene of plum pox virus (PPV) was fused with the leader sequence of the coat protein mRNA (cp) of tobacco mosaic virus by a novel mutagenesis technique which involves reverse transcription of minus-strand RNA [synthesized by in vitro transcription of a double-stranded (ds) cDNA clone], using an ad hoc synthetic oligodeoxynucleotide as primer. The resulting cDNA was rendered ds and cloned into the plasmid, pBluescribe M13+. Transcription of this chimeric construction produced RNA molecules of 1250 nucleotides in length, which were used as messengers in the in vitro protein-synthesizing systems. The major product of this transcript consists of a 36-kDa polypeptide and was identified as the PPV coat protein (CP) by molecular weight estimation and by immunoprecipitation with a polyclonal antiserum to PPV. Transfer of this cDNA via Agrobacterium tumefaciens into plants was successfully performed. Transgenic Nicotiana plants producing the PPV CP were subsequently obtained.
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Affiliation(s)
- M Ravelonandro
- Station de Pathologie Végétale, INRA, La Grande Ferrade, Villenave d'Ornon, France
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123
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Verchot J, Herndon KL, Carrington JC. Mutational analysis of the tobacco etch potyviral 35-kDa proteinase: identification of essential residues and requirements for autoproteolysis. Virology 1992; 190:298-306. [PMID: 1529535 DOI: 10.1016/0042-6822(92)91216-h] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The tobacco etch potyvirus (TEV) polyprotein is processed by three virus-encoded proteinases, termed Nla, HC-Pro, and the 35-kDa proteinase. The 35-kDa proteinase is derived from the amino-terminal region of the polyprotein. Analysis of polyproteins containing beta-glucuronidase fused to the expected carboxy terminus of the 35-kDa proteinase confirmed the previously identified Tyr304-Ser305 dipeptide as the cleavage site between the 35-kDa proteinase and HC-Pro. The 35-kDa proteinase of TEV was unable to catalyze proteolysis when synthetic substrate polyproteins were supplied in a bimolecular or trans reaction, suggesting that processing occurs by an autolytic mechanism. The results of a mutational analysis within the 35-kDa proteolytic domain indicated that His214, Asp223, Ser256, and Asp288 were required for optimal autoproteolytic activity. Replacement of Ser256 with either Thr or Cys resulted in low but detectable proteinase activity, as did substitution of Asp223 and Asp288 with Glu. These results are consistent with the hypothesis that the 35-kDa proteinase resembles cellular serine-type proteinases, with Ser256 functioning as the nucleophilic residue within the active site. Cleavage mediated by the 35-kDa proteinase has been shown previously to occur after polyprotein synthesis in wheat germ extracts and transgenic plants, but not in rabbit reticulocyte lysate. We were able to demonstrate that processing in vitro may require a heat-labile factor present in wheat germ extracts.
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Affiliation(s)
- J Verchot
- Department of Biology, Texas A&M University, College Station 77843
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124
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Laliberté JF, Nicolas O, Chatel H, Lazure C, Morosoli R. Release of a 22-kDa protein derived from the amino-terminal domain of the 49-kDa NIa of turnip mosaic potyvirus in Escherichia coli. Virology 1992; 190:510-4. [PMID: 1529552 DOI: 10.1016/0042-6822(92)91244-o] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The coding region for the precursor 6K-small nuclear inclusion a (NIa) protein and for the NIa protein of turnip mosaic potyvirus (TuMV) were introduced into the plasmid pET-11d for high-level expression in Escherichia coli. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblot analyses of E. coli proteins showed that the NIa protein underwent endoproteolysis and released a 22-kDa polypeptide. NH2-terminal amino acid sequencing of the recombinant 22-kDa protein was performed and was identical to the predicted amino end of the NIa protein. Site-directed mutagenesis confirmed that the hydrolysis was associated with the NIa proteolytic activity and that the proteinase recognized a Glu residue within an amino acid sequence found in the NIa protein which fitted the TuMV consensus cleavage site sequence. Fusion of the 6K protein with the NIa protein partially inhibited the hydrolytic reaction. The recombinant 22-kDa protein is likely the VPg of TuMV.
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Affiliation(s)
- J F Laliberté
- Centre de recherche en virologie, Institut Armand-Frappier, Ville de Laval, Québec, Canada
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125
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Restrepo-Hartwig MA, Carrington JC. Regulation of nuclear transport of a plant potyvirus protein by autoproteolysis. J Virol 1992; 66:5662-6. [PMID: 1501298 PMCID: PMC289134 DOI: 10.1128/jvi.66.9.5662-5666.1992] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The NIa proteinase encoded by tobacco etch potyvirus catalyzes six processing events, three of which occur by an autoproteolytic mechanism. Autoproteolysis is necessary to cleave the boundaries of both NIa and the 6-kDa protein, which is located adjacent to the N terminus of NIa in the viral polyprotein. As a consequence, NIa may exist in a free form or in a transient polyprotein form containing the 6-kDa protein. While the majority of NIa molecules localize to the nuclei of infected cells, a fraction of the NIa pool is attached covalently to the 5' terminus of genomic RNA in the cytoplasm. To determine whether the presence of the 6-kDa protein affects the nuclear transport properties of NIa, we have generated transgenic plants that express genes encoding a reporter enzyme, beta-glucuronidase (GUS), fused to NIa or NIa-containing polyproteins. The NIa/GUS fusion protein was detected by histochemical analysis in the nucleus. Similarly, an NIa/GUS fusion protein that arose by autoproteolysis of a 6-kDa/NIa/GUS polyprotein was found in the nucleus. In contrast, fusion protein consisting of 6-kDa/NIa/GUS, which failed to undergo proteolysis because of the presence of a Cys-to-Ala substitution in the proteolytic domain of NIa, was detected in the cytoplasm. The inhibition of NIa-mediated nuclear transport was not due to the Cys-to-Ala substitution, since this alteration had no effect on translocation in the absence of the 6-kDa protein. These results indicate that the 6-kDa protein impedes nuclear localization of NIa and suggest that subcellular transport of NIa may be regulated by autoproteolysis.
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126
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García JA, Martín MT, Cervera MT, Riechmann JL. Proteolytic processing of the plum pox potyvirus polyprotein by the NIa protease at a novel cleavage site. Virology 1992; 188:697-703. [PMID: 1585641 DOI: 10.1016/0042-6822(92)90524-s] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The expression of potyvirus genomic RNA takes place through translation of its unique long and functional open reading frame into a large polyprotein that undergoes extensive proteolytic processing. Most of the cleavages are performed by the virus-encoded NIa protease, which cuts the polyprotein at defined sites that are characterized by conserved heptapeptide sequences. We have demonstrated in vitro cleavage activity by the plum pox potyvirus (PPV) NIa protease at a novel site, previously identified by sequence analysis, thus allowing a further refinement of the potyviral genetic map. This novel site is located 52 amino acids upstream from the site corresponding to the N-terminus of the CI protein (the NIa cleavage site previously considered the closest to the beginning of the polyprotein). The specificity of the processing was demonstrated by its abolishment when the Gln at position -1 of the cleavage site was changed to His. This novel NIa cleavage site was only partially processed, a characteristic that was not altered when its heptapeptide sequence was modified to become that of the efficiently cleaved NIb-CP junction. On the contrary, substitutions at the nonconserved position +3 had notable effects, positive or negative, on the efficiency of processing. These results show the relevance of sequence and/or conformational context outside the conserved heptapeptide for modulating the cleavage reaction catalyzed by the NIa protease.
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Affiliation(s)
- J A García
- Centro de Biología Molecular (CSIC-UAM), Madrid, Spain
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127
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Abstract
The helper component-proteinase (HC-Pro) encoded by potyviruses functions to cleave the viral polyprotein by an autoproteolytic mechanism at the HC-Pro C-terminus. This protein belongs to a group of viral cysteine-type proteinases and has been shown previously to catalyze proteolysis between a Gly-Gly dipeptide. The amino acid sequence requirements surrounding the HC-Pro C-terminal cleavage site of the tobacco etch virus polyprotein have been investigated using site-directed mutagenesis and in vitro expression systems. A total of 51 polyprotein derivatives, each differing by the substitution of a single amino acid between the P5 and P2' positions, were tested for autoproteolytic activity. Substitutions of Tyr (P4), Val (P2), Gly (P1), and Gly (P1') were found to eliminate or nearly eliminate proteolysis. Substitutions of Thr (P5), Asn (P3), and Met (P2'), on the other hand, were permissive for proteolysis, although the apparent processing rates of some polyproteins containing these alterations were reduced. These results suggest that auto-recognition by HC-Pro involves the interaction of the enzymatic binding site with four amino acids surrounding the cleavage site. Comparison of the homologous sequences of five potyviral polyproteins revealed that the residues essential for processing are strictly conserved, whereas the nonessential residues are divergent. The relationship between HC-Pro and other viral and cellular cysteine-type proteinases is discussed.
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Affiliation(s)
- J C Carrington
- Department of Biology, Texas A&M University, College Station 77843
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128
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Purcifull DE, Hiebert E. Serological relationships involving potyviral nonstructural proteins. ARCHIVES OF VIROLOGY. SUPPLEMENTUM 1992; 5:97-122. [PMID: 1450774 DOI: 10.1007/978-3-7091-6920-9_11] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
This report represents a compilation of many of the publications on antigenic properties of potyviral-specified nonstructural proteins. Polyclonal antisera have been prepared for use in characterization of six nonstructural proteins. These include antisera to the cylindrical inclusion proteins of at least 28 potyviruses, to small nuclear inclusion protein (protease) of four potyviruses, to large nuclear inclusion protein (putative replicase) of three viruses, helper component-protease or amorphous inclusion protein of at least four viruses, to the P1 protein (located at the N-terminus of the polyprotein) of one virus, and to the P3 protein (located between helper component protease and cylindrical inclusion protein) of one virus. Monoclonal antibodies also have been prepared to several of these nonstructural proteins. The evidence thus far indicates that cylindrical inclusions of different potyviruses have both conserved and unique epitopes. Nuclear inclusion proteins and amorphous inclusion proteins also may have conserved and unique epitopes. Antigenic relationships of potyviral nonstructural proteins have potential for the identification and classification of potyviruses.
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Affiliation(s)
- D E Purcifull
- Department of Plant Pathology, University of Florida, Gainesville
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129
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Atreya CD. Application of genome sequence information in potyvirus taxonomy: an overview. ARCHIVES OF VIROLOGY. SUPPLEMENTUM 1992; 5:17-23. [PMID: 1450734 DOI: 10.1007/978-3-7091-6920-9_2] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The application of protein and nucleic acid sequence analysis in evolutionary and phylogenetic studies is well established. Available sequence information for the 5' untranslated region of potyviruses including the fungus-transmitted barley yellow mosaic virus (BaYMV) RNA-1 suggests that a 12-nucleotide conserved sequence, the "potybox" is unique to this group. Various non-structural proteins of potyviruses share considerable "signature" sequence homology across a broad spectrum of unrelated viruses, which makes their value limited to "supergroup" or "superfamily" identity. However, in potyviruses, the coat-protein N-terminal sequences and 3' noncoding regions are variable among viruses, but similar among strains of the same virus. This suggests that these sequences may be an accurate marker of genetic relatedness. Until complete genome sequences from a large number of potyviruses become available and their value in systematics is tested, coat protein and 3' noncoding regions remain as the choice of taxonomic indicators. The reason being, that cloning and sequencing of the coat-protein gene and 3' noncoding regions are less complicated and time consuming and the sequences show significant differences among the virus species within the family Potyviridae.
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Affiliation(s)
- C D Atreya
- Department of Plant Pathology, University of Kentucky, Lexington
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130
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Rodríguez-Cerezo E, Shaw JG. Two newly detected nonstructural viral proteins in potyvirus-infected cells. Virology 1991; 185:572-9. [PMID: 1962438 DOI: 10.1016/0042-6822(91)90527-i] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The existence of two viral RNA-encoded proteins in cells infected with tobacco vein mottling potyvirus (TVMV) has been demonstrated. One of the proteins (named 34K) maps at the N-terminus of the TVMV polyprotein and the other (42K) between the helper component and cylindrical inclusion proteins; both had previously been predicted in the consensus potyviral genetic map. The 34K and 42K coding regions of TVMV were cloned separately in a bacterial expression vector and the proteins were isolated from transformed Escherichia coli. These were used to raise polyclonal antibodies which reacted specifically with proteins of the expected size in immunoblots of extracts of TVMV-infected tobacco leaves and protoplasts. In addition to 42K, the anti-42K serum detected similar amounts of a second protein of apparent size 37 kDa that was absent in 42K-expressing bacteria. Both 34K and 42K were present predominantly in membrane-enriched fractions of extracts of TVMV-infected tobacco leaves. Computer analysis of the deduced amino acid sequence of 42K suggests that this viral protein may be an integral transmembrane protein.
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