Culver J N, Lehto K, Close S M, Hilf M E, Dawson W O
Department of Plant Pathology, University of California, Riverside 92521.
Proc Natl Acad Sci U S A. 1993 Mar 1;90(5):2055-9. doi: 10.1073/pnas.90.5.2055.
Alterations in the genomic position of the tobacco mosaic virus (TMV) genes encoding the 30-kDa cell-to-cell movement protein or the coat protein greatly affected their expression. Higher production of 30-kDa protein was correlated with increased proximity of the gene to the viral 3' terminus. A mutant placing the 30-kDa open reading frame 207 nucleotides nearer the 3' terminus produced at least 4 times the wild-type TMV 30-kDa protein level, while a mutant placing the 30-kDa open reading frame 470 nucleotides closer to the 3' terminus produced at least 8 times the wild-type TMV 30-kDa protein level. Increases in 30-kDa protein production were not correlated with the subgenomic mRNA promoter (SGP) controlling the 30-kDa gene, since mutants with either the native 30-kDa SGP or the coat protein SGP in front of the 30-kDa gene produced similar levels of 30-kDa protein. Lack of coat protein did not affect 30-kDa protein expression, since a mutant with the coat protein start codon removed did not produce increased amounts of 30-kDa protein. Effects of gene positioning on coat protein expression were examined by using a mutant containing two different tandemly positioned tobamovirus (TMV and Odontoglossum ringspot virus) coat protein genes. Only coat protein expressed from the gene positioned nearest the 3' viral terminus was detected. Analysis of 30-kDa and coat protein subgenomic mRNAs revealed no proportional increase in the levels of mRNA relative to the observed levels of 30-kDa and coat proteins. This suggests that a translational mechanism is primarily responsible for the observed effect of genomic position on expression of 30-kDa movement and coat protein genes.
编码30 kDa细胞间运动蛋白或外壳蛋白的烟草花叶病毒（TMV）基因的基因组位置改变极大地影响了它们的表达。30 kDa蛋白的更高产量与该基因靠近病毒3'末端的程度增加相关。一个将30 kDa开放阅读框置于距3'末端近207个核苷酸处的突变体产生的野生型TMV 30 kDa蛋白水平至少是其4倍，而一个将30 kDa开放阅读框置于距3'末端近470个核苷酸处的突变体产生的野生型TMV 30 kDa蛋白水平至少是其8倍。30 kDa蛋白产量的增加与控制30 kDa基因的亚基因组mRNA启动子（SGP）无关，因为在30 kDa基因前带有天然30 kDa SGP或外壳蛋白SGP的突变体产生的30 kDa蛋白水平相似。外壳蛋白的缺失不影响30 kDa蛋白的表达，因为一个去除了外壳蛋白起始密码子的突变体并没有产生更多的30 kDa蛋白。通过使用一个含有两个不同串联排列的烟草花叶病毒（TMV和齿舌兰环斑病毒）外壳蛋白基因的突变体来研究基因定位对外壳蛋白表达的影响。只检测到了从最靠近病毒3'末端的基因表达的外壳蛋白。对30 kDa和外壳蛋白亚基因组mRNA的分析显示，相对于观察到的30 kDa和外壳蛋白水平，mRNA水平没有成比例增加。这表明翻译机制是基因组位置对30 kDa运动蛋白和外壳蛋白基因表达产生观察到的影响的主要原因。
