Functions of the helper component-proteinase during tobacco etch potyvirus infection /
The tobacco etch potyvirus (TEV) helper component-proteinase (HC-Pro) is a multifunctional protein involved in many steps of the virus life cycle. This dissertation focuses on the interrelationship of the HC-Pro functions during TEV infection. The C- terminal domain of HC-Pro is a cysteine type prot...
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
1999.
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| Subjects: | |
| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=733678051&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | The tobacco etch potyvirus (TEV) helper component-proteinase (HC-Pro) is a multifunctional protein involved in many steps of the virus life cycle. This dissertation focuses on the interrelationship of the HC-Pro functions during TEV infection. The C- terminal domain of HC-Pro is a cysteine type proteinase that autocatalytically cleaves between itself and the P3 protein. To determine the requirement for HC-Pro specific processing during viral replication, mutations resulting in amino acid substitutions in the proteolytic domain and cleavage site motif were introduced into the viral genome. In all cases, when HC-Pro processing was debilitated the mutant genome was amplification- defective. Amplification capabilities of the HC-Pro processing defective mutant genomes were not restored by supplying HC-Pro in trans or by inserting the coding sequence for a heterozygous cleavage site recognized the TEV NIa proteinase between HC-Pro and P3. These results suggest that an active HC-Pro proteinase is required in cis for TEV genome amplification. To investigate the genome amplification and long-distance movement functions of HC-Pro, systematic alanine-scanning mutagenesis was performed on the central and proteolytic domains of the protein. Analysis of these mutants indicated the central domain between residues 126 and 300 is necessary for efficient genome amplification and long- distance movement of TEV. The amplification phenotype of the central domain mutants was characterized by a progressive shut-off during the course of infection. Wild-type HC-Pro supplied in trans was able to partially restore amplifications and movement functions of the central domain alanine-scanning mutants. These results were consistent with the hypothesis that HC-Pro serves as a suppressor of one or more host defense responses. In fact, P1/HC-Pro was demonstrated to act as a suppressor of posttranscriptional gene silencing (PTGS), a mechanism that appears to function as an adaptive antiviral response in plants. Genetic crosses between transgenic tobacco plants expressing P1/HC-Pro and transgenic tobacco plants in which the transient was shown to exhibit PTGS revealed the P1/ HC-PI-O transcend suppressed PTGS of the other transcend. |
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| Item Description: | Vita. "Major Subject: Biology". |
| Physical Description: | x, 127 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilm Inc. |
| Bibliography: | Includes bibliographical references (leaves 102-125). |