Browsing by Subject "rRNA processing"
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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 A novel protein shared by RNase MRP and RNase P(The RNA Society, 1997-04) Chu, S.; Zengel, J. M.; Lindahl, L.We have isolated suppressors of the temperature-sensitive rRNA processing mutation rrp2-2 in Saccharomyces cerevisiae. A class of extragenic suppressors was mapped to the YBR257w reading frame in the right arm of Chromosome II. Characterization of this gene, renamed POP4, shows that the gene product is necessary both for normal 5.8S rRNA processing and for processing of tRNA. Immunoprecipitation studies indicate that Pop4p is associated with both RNase MRP and RNase P. The protein is also required for accumulation of RNA from each of the two ribonucleoprotein particles.Item RNase MRP is required for entry of 35S precursor rRNA into the canonical processing pathway(The RNA Society, 2009-07) Lindahl, Lasse; Bommankanti, Ananth; Li, Xing; Hayden, Lauren; Jones, Adrienne; Khan, Miriam; Oni, Tolulope; Zengel, Janice M.RNase MRP is a nucleolar RNA–protein enzyme that participates in the processing of rRNA during ribosome biogenesis. Previous experiments suggested that RNase MRP makes a nonessential cleavage in the first internal transcribed spacer. Here we report experiments with new temperature-sensitive RNase MRP mutants in Saccharomyces cerevisiae that show that the abundance of all early intermediates in the processing pathway is severely reduced upon inactivation of RNase MRP. Transcription of rRNA continues unabated as determined by RNA polymerase run-on transcription, but the precursor rRNA transcript does not accumulate, and appears to be unstable. Taken together, these observations suggest that inactivation of RNase MRP blocks cleavage at sites A0, A1, A2, and A3, which in turn, prevents precursor rRNA from entering the canonical processing pathway (35S > 20S + 27S > 18S + 25S + 5.8S rRNA). Nevertheless, at least some cleavage at the processing site in the second internal transcribed spacer takes place to form an unusual 24S intermediate, suggesting that cleavage at C2 is not blocked. Furthermore, the long form of 5.8S rRNA is made in the absence of RNase MRP activity, but only in the presence of Xrn1p (exonuclease 1), an enzyme not required for the canonical pathway. We conclude that RNase MRP is a key enzyme for initiating the canonical processing of precursor rRNA transcripts, but alternative pathway(s) might provide a backup for production of small amounts of rRNA.