Lindahl L, Fretz S, Epps N, Zengel J M
Department of Biological Sciences, University of Maryland Baltimore County, Baltimore 21250, USA.
RNA. 2000 May;6(5):653-8. doi: 10.1017/s1355838200992574.
RNase MRP and RNase P are both ribonucleoprotein enzymes performing endonucleolytic cleavage of RNA. RNase MRP cleaves at a specific site in the precursor-rRNA transcript to initiate processing of the 5.8S rRNA. RNase P cleaves precursor tRNAs to create the 5' end of the mature tRNAs. In spite of their different specificities, the two RNases have significant structural similarities. For example, the two enzymes in Saccharomyces cerevisiae share eight protein subunits; only one protein is unique to each enzyme. The RNA components of the two nucleases also show striking secondary-structure similarity. To begin to characterize the role of the RNA subunits in enzyme function and substrate specificity, we swapped two hairpin structures (MRP3 and P3) between RNase MRP RNA and RNase P RNA of S. cerevisiae. The hairpins in the two enzymes could be exchanged without loss of function or specificity. On the other hand, when the MRP3 hairpin in RNase MRP of S. cerevisiae was replaced with the corresponding hairpin from the RNA of Schizosaccharomyces pombe or human RNase MRP, no functional enzyme was assembled. We propose that the MRP3 and P3 hairpins in S. cerevisiae perform similar functions and have coevolved to maintain common features that are different from those of MRP3 and P3 hairpins in other species.
核糖核酸酶MRP和核糖核酸酶P都是进行RNA内切酶切割的核糖核蛋白酶。核糖核酸酶MRP在前体rRNA转录本的特定位点进行切割，以启动5.8S rRNA的加工。核糖核酸酶P切割前体tRNA以产生成熟tRNA的5'端。尽管它们具有不同的特异性，但这两种核糖核酸酶在结构上有显著的相似性。例如，酿酒酵母中的这两种酶共有八个蛋白质亚基；每种酶只有一种独特的蛋白质。这两种核酸酶的RNA组分也显示出惊人的二级结构相似性。为了开始表征RNA亚基在酶功能和底物特异性中的作用，我们在酿酒酵母的核糖核酸酶MRP RNA和核糖核酸酶P RNA之间交换了两个发夹结构（MRP3和P3）。两种酶中的发夹可以交换，而不会丧失功能或特异性。另一方面，当酿酒酵母核糖核酸酶MRP中的MRP3发夹被粟酒裂殖酵母或人核糖核酸酶MRP的RNA中的相应发夹取代时，没有组装出功能性酶。我们提出，酿酒酵母中的MRP3和P3发夹具有相似的功能，并且已经共同进化以维持与其他物种中MRP3和P3发夹不同的共同特征。
