Gomatos P J, Prakash O, Stamatos N M
J Virol. 1981 Jul;39(1):115-24. doi: 10.1128/JVI.39.1.115-124.1981.
We reported previously that polycytidylate [poly(C)]-dependent RNA polymerase activity was a property of small spherical or triangular reovirus-specific particles which sedimented at 13 to 19S and were composed solely of the reovirus protein, sigma NS. Depending on the fraction of cellular extracts from which they were obtained, these particles exhibited marked differences in stability. Most 13 to 19S particles from a particular fraction repeatedly disaggregated into smaller 4 to 5S subunits with no enzymatic activity. Disruption of many particles could be prevented and polymerase activity retained after these particles had bound different single-stranded (ss) RNAs. Our previous results indicated that there was heterogeneity among the 13 to 19S particles in that possession of poly(C)-dependent RNA polymerase activity was a property of only some. Support for this heterogeneity was derived from the demonstration in this report that there were at least three types of binding sites present within particles in any purified preparation: (i) those binding only poly(C); (ii) those binding only reovirus ss RNAs; and (iii) those binding one or the other, but not both at the same time. It is suggested that only those particles able to bind either poly(C) or reovirus ss RNAs had poly(C)-dependent RNA polymerase activity, as reovirus ss RNAs markedly inhibited the polymerase activity. All three size classes of reovirus ss RNAs were equally effective in binding, but once bound, they were not copied. It is possible that heterogeneity in binding capacity of different particles comprised of only one protein, sigma NS, could result from the ability of subunits containing this protein to assemble into slightly different 13 to 19S particles with specificity of binding or polymerase activity conferred by the configuration of the assembled particles. The high capacity of sigma NS to bind many different nucleic acids with some specificity suggests that these particles may act during infection as condensing agents to bring together 10 reovirus ss RNA templates in preparation for double-stranded RNA synthesis.
我们之前报道过，聚胞苷酸[poly(C)]依赖性RNA聚合酶活性是小的球形或三角形呼肠孤病毒特异性颗粒的一种特性，这些颗粒在13至19S处沉降，并且仅由呼肠孤病毒蛋白sigma NS组成。根据从中获得它们的细胞提取物的组分不同，这些颗粒在稳定性上表现出显著差异。来自特定组分的大多数13至19S颗粒会反复解聚成没有酶活性的较小的4至5S亚基。在这些颗粒结合了不同的单链(ss)RNA后，可以防止许多颗粒的破坏并保留聚合酶活性。我们之前的结果表明，13至19S颗粒之间存在异质性，因为只有一些颗粒具有聚胞苷酸依赖性RNA聚合酶活性。本报告中的证据支持了这种异质性，即在任何纯化制剂的颗粒内至少存在三种类型的结合位点：(i)仅结合聚胞苷酸的位点；(ii)仅结合呼肠孤病毒ss RNA的位点；(iii)结合其中一种但不同时结合两者的位点。有人提出，只有那些能够结合聚胞苷酸或呼肠孤病毒ss RNA的颗粒才具有聚胞苷酸依赖性RNA聚合酶活性，因为呼肠孤病毒ss RNA会显著抑制聚合酶活性。呼肠孤病毒的所有三种大小类别的ss RNA在结合方面同样有效，但一旦结合，它们就不会被复制。仅由一种蛋白sigma NS组成的不同颗粒在结合能力上的异质性，可能是由于含有该蛋白的亚基能够组装成略有不同的13至19S颗粒，其结合特异性或聚合酶活性由组装颗粒的构型赋予。sigma NS以一定特异性结合许多不同核酸的高能力表明，这些颗粒在感染期间可能作为凝聚剂，将10个呼肠孤病毒ss RNA模板聚集在一起，为双链RNA合成做准备。
