Study of post-translational modification of plant virus proteins

芜菁花叶病毒（TuMV）是芜菁花叶病毒科芜菁花叶病毒属的一员，在世界范围内引起疾病。本研究的目的是研究TuMV蛋白的翻译后修饰。多型病毒的单株基因组由一个单链、约10kb的正义RNA分子组成，该分子含有一个开放阅读框，其翻译产物由顺式和反式激活的病毒蛋白酶处理，产生成熟的病毒蛋白。从5个重叠的cDNA克隆和病毒RNA直接测序中确定了TuMV日本株RNA基因组的完整核苷酸序列。该RNA序列长度为9833个核苷酸，不包括3'端poly (a) trail。位于130-132位的AUG三联体被指定为翻译基因组大小的病毒多蛋白的起始密码子，该多蛋白将由3164个氨基酸残基组成。通过培养抗P1、辅助组分蛋白酶（HC-Pro）、P3、细胞质包涵体（CI）和外壳蛋白（CP）的血清，研究了TuMV蛋白在芜菁和烟叶亚细胞部位的存在。在细胞壁富集部位检测到HC-Pro蛋白，提示HC-Pro蛋白可能参与了TuMV的细胞间运动功能。此外，用抗HC-Pro蛋白的血清追踪了完整tumv感染叶片中HC-Pro蛋白积累的时间过程。CP在接种后逐渐积累，而HC-Pro在接种后7天逐渐积累，然后逐渐减少。

Turnip mosaic virus (TuMV), a member of the genus Potyvirus in the familiy Potyviridae, causes disease world wide. The purpose of this study was to investigate post-translational modification of TuMV proteins. The monopartite genome of potyviruses consists of a single-stranded, positive-sense approximately 10kb RNA molecule containing a single open reading frame whose translation product is processed by cis-and trans-activating viral proteinases to yield mature viral proteins. The complete nucleotide sequence of the RNA genome of TuMV Japanese strain has been determined from five overlapping cDNA clones and by direct sequencing of viral RNA.The RNA sequence was 9833 nucleotides in length, excluding a 3' terminal poly (A) trail. An AUG triplet at position 130-132 was assigned as the initiation codon for the translation of the genome size viral polyprotein which would consist of 3164 amino acid residues. The presence of TuMV proteins in subcellular fractions of leaves of turnip and Nicotiana benthamiana plants was investigated with the antisera raised against P1, helper-component proteinase (HC-Pro), P3, cytoplasmic inclusion (CI) and coat proteins (CP). HC-Pro protein was detected at the cell wall-enriched fraction and the result indicates that HC-Pro protein may involve the function of cell-to-cell movement of TuMV.Furthermore, antiserum raised against HC-Pro protein was used to follow the time course of accumulation of HC-Pro protein in intact TuMV-infected leaves. CP gradually accumulated following inoculation whereas HC-Pro accumulated up to 7 day p.i.and then gradually decreased.