Nothwang H G, Coux O, Bey F, Scherrer K
Institut Jacques Monod, Université Paris, France.
Biochem J. 1992 Nov 1;287 ( Pt 3)(Pt 3):733-9. doi: 10.1042/bj2870733.
Prosomes are ribonucleoprotein particles constituted by a variable set of about 20 proteins found associated with untranslated mRNA. In addition, they contain a small RNA, the presence of which has been an issue of controversy for a long time. The intact particles have a multicatalytic proteinase (MCP) activity and are very stable; we have never observed autodigestion of the particle by its intrinsic proteinase activity. Surprisingly it was found that Zn2+ and Cu2+ ions at concentrations of 0.1-1 mM disrupt the prosome particles isolated from HeLa cells and duck erythroblasts and abolish instantaneously its MCP activity, without altering the two-dimensional electrophoretic pattern of the constituent proteins. Fe2+, however, seems to induce autodegradation rather than dissociation of the prosome constituents. Most interestingly, protein or oligopeptide substrates protect the particle and its proteinase activity from disruption by Zn2+ or Cu2+. Nuclease-digestion assays reveal that the prosomal RNA, which is largely resistant in the intact particle, becomes digestible after dissociation of prosomes by Zn2+. These data give, for the first time, unambiguous proof of the presence of an RNA in the particle. Furthermore, they demonstrate a structure-function relationship between the complex and its enzyme activity, which seems to be based on the particle as an entity and not on the single constituent proteins.
前体微粒是核糖核蛋白颗粒，由大约20种可变的蛋白质组成，这些蛋白质与未翻译的mRNA相关。此外，它们还含有一种小RNA，其存在长期以来一直存在争议。完整的颗粒具有多催化蛋白酶（MCP）活性且非常稳定；我们从未观察到颗粒因其内在蛋白酶活性而发生自消化。令人惊讶的是，发现浓度为0.1 - 1 mM的Zn2+和Cu2+离子会破坏从HeLa细胞和鸭红细胞中分离出的前体微粒，并立即消除其MCP活性，而不会改变组成蛋白质的二维电泳图谱。然而，Fe2+似乎会诱导前体微粒成分的自降解而不是解离。最有趣的是，蛋白质或寡肽底物可保护颗粒及其蛋白酶活性免受Zn2+或Cu2+的破坏。核酸酶消化试验表明，在完整颗粒中具有很大抗性的前体RNA在Zn2+使前体微粒解离后变得可消化。这些数据首次明确证明了颗粒中存在RNA。此外，它们证明了该复合物与其酶活性之间的结构 - 功能关系，这似乎基于颗粒作为一个整体，而不是单个组成蛋白质。
