Factors Affecting the Accumulation of Bamboo Mosaic Potexvirus-associated Defective RNAs
| Autor: | Lee, Shu-Chuan, 李淑娟 |
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| Rok vydání: | 2000 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 88 Bamboo mosaic virus (BaMV) belongs to Potexvirus group and has a single-stranded, positive-sense RNA molecule. Genome of BaMV is 6.4 kb in length and contains five open reading frames (ORFs). Naturally occurring defective RNAs (D RNAs) of BaMV are composed of the 5’ and 3’ termini of BaMV genome and contain an ORF. D20, one of BaMV D RNAs, had the highest level of accumulation than others in protoplast assay. D20-derived mutants were constructed by means of polymerase chain reaction-directed mutagenesis. Protoplast infection assays were used to evaluate the biological activity of D20-derived mutants. The results suggested that the maintenance of the ORF is crucial for the accumulation of BaMV D RNAs in vivo. In addition, the length of the ORF influenced the accumulation of D RNAs, and must be no less than 99 amino acids in order to maintain their biological activities. When the sequences of the ORF was replaced by BaMV coat protein gene or foreign EGFP gene, the mutants were nonviable although their ORF lengths similar to D20. The above results indicated that not only the lengths of the ORF but also the sequences within ORF are important for the accumulation of BaMV D RNA. According to the experimental results of D20 deletion mutants, the minimum sequences required for biological activities of BaMV D RNAs are from regions nt 1-551 and nt 936-1118. D20 mutants with nt 388-551 deleted lost their viabilities. This result suggested that these sequences may contain cis-acting sequence of replication. Although nt 551-936 is not essential for replication, it could increase the level of accumulation of D RNAs. Taken together, the ORF sequence of D RNAs can not be replaced by other genes, and both the lengths and the sequences of the ORF influence the accumulation of BaMV D RNAs in vivo. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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