The POP1 gene encodes a protein component common to the RNase MRP and RNase P ribonucleoproteins.

Abstract

Two forms of the yeast 5.8S rRNA are generated from a large precursor by distinct processing pathways. Cleavage at site A3 is required for synthesis of the major, short form, designated 5.8S(S), but not for synthesis of the long form, 5.8S(L). To identify components required for A3 cleavage, a bank of temperature-sensitive lethal mutants was screened for those with a reduced ratio of 5.8S(S):5.8S(L). The pop1-1 mutation (for processing of precursor RNAs) shows this phenotype and also inhibits A3 cleavage. The pre-rRNA processing defect of pop1-1 strains is similar to that reported for mutations in the RNA component of RNase MRP; we show that a mutation in the RNase MRP RNA also inhibits cleavage at site A3. This is the first site shown to require RNase MRP for cleavage in vivo. The pop1-1 mutation also leads to a block in the processing of pre-tRNA that is identical to that reported for mutations in the RNA component of RNase P. The RNA components of both RNase MRP and RNase P are underaccumulated in pop1-1 strains at the nonpermissive temperature, and immunoprecipitation demonstrates that POPlp is a component of both ribonucleoproteins.The POP1 gene encodes a protein with a predicted molecular mass of 100.5 kD and is essential for viability.POPlp is the first protein component of the nuclear RNase P or RNase MRP for which the gene has been cloned.[Key Words: POP1 gene; RNase MRP; RNase P; S. cerevisiae; RNA processing] Received April 4, 1994; revised version accepted May 9, 1994.Two ribonucleoprotein (RNP) complexes are known to have endoribonuclease (RNase) activity. These are the RNase P and RNase mitochondrial RNA processing (MRP) RNPs.All pre-tRNAs are transcribed with 5' and 3' extensions, and some contain intervening sequences that are removed to produce the mature tRNAs. RNase P is responsible for the 5' processing of pre-tRNAs in eubacteria, archaebacteria, and eukaryotes (for review, see Altman 1989;Dart et al. 1992;Altman et al. 1993). RNase P also processes the precursor of the 4.5S RNA in Escherichia coli (for review, see by Altman et al. 1993) but has not been reported to have substrates other than pretRNAs in archaebacteria or eukaryotes. The RNA component of eubacterial RNase P has catalytic activity in vitro in the absence of protein cofactors. In contrast, the RNA components of archaebacterial (Nieuwlandt et al. 1991;LaGrandeur et al. 1993) and eukaryotic RNase P have not been found to be catalytic in the absence of proteins, despite their considerable structural homology to the eubacterial RNAs. E. coli RNase P contains a single protein, designated C5, which is small (119 amino acids, 13.8 kD) and highly basic. This protein cofactor is required for RNase P activity in vivo and greatly stimulates activity in vitro. The protein plays important roles in the release of the product, the mature tRNA, from the enzyme, which is the rate-limiting step for the RNA catalyzed reaction in vitro (Reich et al. 1988;Tallsj6 and Kirsebom 1993), and in the binding of suboptimal substrates, including the 4.5S RN...

The 18S rRNA dimethylase Dim1p is required for pre-ribosomal RNA processing in yeast.

“…The 27SA' pre-rRNA cannot be detected by Northern hybridization, but primer extension through site A3, the 5' end of 27SAr, shows that its accumulation is unaffected in the GAL::diml strain (data not shown). The levels of the 5.8s rRNA and its 7s precursor are also unaffected in the GAL::diml strain, and no alteration was detected in the relative use of the alternative processing pathways that lead to the formation of the long and short forms of 5.8s rRNA , Lygerou et al 1994) (data not shown).…”

“…2, ITSlA3' lanes), demonstrating that the 32s pre-rRNA, or larger precursors, is methylated. Similarly, mutations in RRP2 (NMEI] or POPI, which encode the RNA and protein components of RNase MRP, respectively, also delay synthesis of 20s pre-rRNA (Lygerou et al 1994) and lead to methylation of the 32s pre-rRNA (data not shown). Because the processing of 32s to 20s pre-rRNA is nucleolar, methylation can occur in the nucleolus.…”

Partially Processed pre-rRNA Is Preserved in Association with Processing Components in Nucleolus-derived Foci during Mitosis

“…RNase MRP is implicated in the cleavage of pre-rRNA at site A3 within ITS1 (Lygerou et al, 1994). RNase P participates in cleavages in the 5Ј-ETS, ITS1, and ITS2 of the primary 35S pre-rRNA transcript in yeast (Chamberlain et al, 1996;Stolc and Altman, 1997).…”

Purification and Characterization of Mitochondrial Ribonuclease P from Aspergillus Nidulans

“…Thirdly, a previous report identifying multiprotein subunit association with RNase MRP (mitochondrial RNA processing) activity also supports this notion. RNase MRP enzyme is a ribonucleoprotein that is closely related to RNase P: they contain RNA components having secondary structure similarities 1401, share a common epitope 1411 and a protein component [42], and have nuclear-encoded protein subunits. Pulse-chase labeling of HeLa cells and purification of the RNase mitochondrial RNA processing enzyme revealed that about 10 polypeptides, with molecular masses in the range 10-100 kDa, were copurified with the enzyme activity 1431.…”