Browsing by Subject "RNA structure"
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Item Functional equivalence of hairpins in the RNA subunits of RNase MRP and RNase P in Saccharomyces cerevisiae(The RNA Society, 2000-05) Lindahl, L.; Fretz, S.; Epps, N.; Zengel, J. M.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 59 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.Item Surprising flexibility of leader RNA determinants for r-protein L4-mediated transcription termination in the Escherichia coil S10 operon(The RNA Society, 2002-05) Zengel, Janice M.; Sha, Yizhong; Lindahl, LasseEscherichia coli ribosomal protein L4 autogenously regulates transcription of the S10 operon, which encodes L4 and 10 other ribosomal proteins. Regulation results from L4-stimulated premature transcription termination at a U-rich site in the untranslated leader. The process requires transcription factor NusA. Here we report a detailed analysis of the RNA requirements for NusA-dependent, L4-mediated transcription control. We found that efficient regulation requires multiple features of the S10 leader, including two hairpins, called HD and upper HE, a connecting tether, and a U-rich sequence at the distal side of HE. As expected, regulation was optimal when all 7 Us were maintained in the U4CGU3 sequence at the termination site. However, despite the apparent specificity of L4 action on only the S10 operon, there is surprising flexibility at the primary sequence level for the HD-tether-HE region. Changes in the sequence of non-base-paired nucleotides flanking the HD hairpin or an A at the second position of the HD loop reduced L4 regulation, but other changes had little or no effect. Furthermore, generic hairpins from other RNAs could replace the natural HD and upper HE hairpins with little or no reduction of L4 control, suggesting that the secondary structure elements are also relatively generic. The lack of specific sequence requirements suggests that L4 may recognize multiple elements within this region of the nascent leader.