Hajimorad M R, Kurath G, Randles J W, Francki R I
Department of Crop Protection, Waite Agricultural Research Institute, University of Adelaide, Glen Osmond, South Australia.
J Gen Virol. 1991 Dec;72 ( Pt 12):2885-93. doi: 10.1099/0022-1317-72-12-2885.
A local lesion isolate of alfalfa mosaic virus (AMV-N20) from lucerne was found to encapsidate two extra RNAs in addition to the four major RNAs (RNA1, -2, -3 and -4). These were resolved by gel electrophoresis both under native conditions and after glyoxal denaturation. The RNA with an electrophoretic mobility between that of RNAs 2 and 3 was designated RNA31, that between RNAs 3 and 4 was designated RNA3s. Sucrose density gradient centrifugation analysis of AMV-N20 showed six instead of the normal four nucleoprotein components, the additional two presumably representing encapsidated RNAs 31 and 3s. RNAs 31 and 3s were both shown by Northern blot hybridization to be unrelated to host plant RNA and to contain the AMV coat protein gene sequence, which resides in RNA3. Primer extension of the RNAs 31 and 3s using a primer complementary to the 3' common terminus of all genomic AMV RNAs provided further evidence that they contained AMV sequences. RNA31 represents an addition of about 255 nucleotides, compared with RNA3, and RNA3s represents a loss of about 308 nucleotides. The coat proteins of variants encapsidating either RNA31, -3 or -3s had the same Mr indicating that the addition or deletion of the nucleotides was outside the coat protein gene. Serial mechanical passage of AMV-N20 over 5 years in four host species led both to changes in the composition of the RNA3 mixture, and to changes in symptom severity. For example, following passage in Nicotiana clevelandii, RNA3 was lost whereas passage in either N. glutinosa, Chenopodium quinoa or C. amaranticolor resulted in the loss of RNA31. No association was found between the changes in RNA3 and phenotypic changes that resulted from continuous passage for 5 years. Phenotypic changes with passage are thus presumably determined by mutations elsewhere in the virus genome.
从紫花苜蓿中分离出的苜蓿花叶病毒（AMV-N20）的一个局部病变分离株，除了四个主要RNA（RNA1、-2、-3和-4）外，还包裹了另外两个RNA。这些RNA在天然条件下以及乙二醛变性后通过凝胶电泳得以分离。电泳迁移率介于RNA2和RNA3之间的RNA被命名为RNA31，介于RNA3和RNA4之间的RNA被命名为RNA3s。对AMV-N20进行蔗糖密度梯度离心分析显示有六个而非正常的四个核蛋白组分，额外的两个组分推测代表包裹的RNA31和RNA3s。通过Northern印迹杂交表明，RNA31和RNA3s均与宿主植物RNA无关，并包含位于RNA3中的AMV外壳蛋白基因序列。使用与所有基因组AMV RNA的3'共同末端互补的引物对RNA31和RNA3s进行引物延伸，进一步证明它们包含AMV序列。与RNA3相比，RNA31大约增加了255个核苷酸，而RNA3s大约缺失了308个核苷酸。包裹RNA31、-3或-3s的变体的外壳蛋白具有相同的相对分子质量，这表明核苷酸的添加或缺失位于外壳蛋白基因之外。AMV-N20在四种宿主植物中连续机械传代5年，导致RNA3混合物的组成发生变化，同时症状严重程度也发生变化。例如，在克利夫兰烟草上连续传代后，RNA3消失，而在黏毛烟草、藜麦或苋色藜上连续传代则导致RNA31消失。连续传代5年导致的RNA3变化与表型变化之间未发现关联。因此，传代导致的表型变化可能是由病毒基因组其他位置的突变决定的。
