High impact information on NOP2

• Nop2 is an essential RNA cytosine methyltransferase responsible for the methylation of cytosine 2870 of 25S rRNA. [1]
• Two highly conserved cysteine residues in the domain IV and domain VI are indispensable for the methylation reaction. [1]
• The lack of methylation at C2870 influences the processing of rRNA [1].
• The consequences of overexpressing NOP2 from the GAL10 promoter on a multicopy plasmid were investigated [2].
• NOP2 mRNA levels also increase during the onset of growth, accompanied by a similar increase in the levels of TCM1 mRNA [2].
• We have isolated a gene (NOP2) encoding a nucleolar protein during a search for previously unidentified nuclear proteins in the yeast Saccharomyces cerevisiae [2].
• Although NOP2 overexpression produced no discernible growth phenotype and had no effect on ribosome subunit synthesis, overexpression was found to influence the morphology of the nucleolus, as judged by electron microscopy [2].
• The protein encoded by NOP2 (Nop2p) has a predicted molecular mass of 70 kD, migrates at 90 kD by SDS-PAGE, and is essential for cell viability [2].

Biological context of NOP2

• The nucleolar protein Nop2p is an essential gene product that is required for pre-rRNA processing and ribosome biogenesis in Saccharomyces cerevisiae (Hong, B. et al., 1997, Mol. Cell. Biol., 17, 378-388) [3].
• Although Nop2p depletion lengthens the half-life of 27S pre-RNA, methylation of UmGm psi UC2922 in 27S pre-rRNA is low during Nop2p depletion [4].
• Conditional lethality is not due to rapid turnover of mutant Nop2p proteins at 37 degrees C. Each allele contains between seven and 14 amino acid substitutions and one possesses a nonsense mutation near the C-terminus [5].
• Using molecular genetic techniques, we have generated and characterized six temperature sensitive (ts) alleles of nop2 [5].

Anatomical context of NOP2

• Repression of NOP2 expression lengthens the doubling time of this strain about fivefold and reduces steady-state levels of 60S ribosomal subunits, 80S ribosomes, and polysomes [4].
• Analysis of subcellular fractions indicates that Nop2p is located primarily in the nucleus, and nuclear fractionation studies suggest that Nop2p is associated with the nucleolus [2].

Associations of NOP2 with chemical compounds

• It physically interacts with rRNA processing factors, notably Cbf5p and Nop2p, and co-fractionates specifically with pre-60 S particles on sucrose gradients [6].
• A conserved motif in the yeast nucleolar protein Nop2p contains an essential cysteine residue [7].
• Nop2p function was abolished by conversion of Cys424 into either alanine or serine [7].
• The crucial role of Cys424 in Nop2p is intriguing, due to the critical roles that cysteine residues adjacent to a proline have in a number of nucleotide-modifying enzymes [7].
• All of the other Nop2p mutations tested sustained yeast viability, including glycine replacement of Pro423 and the conversion of a second conserved cysteine into alanine [7].

Other interactions of NOP2

• Evidence for the predicted accumulation of protein-RNA complexes following mutation of the assisting cysteine has been obtained with Nop2p and a known tRNA m(5)C methyltransferase called Ncl1p (Trm4) [8].
• The model was conceived as a possible explanation for the effects of mutations that change the conserved cysteines in Nop2p, an apparent RNA m(5)C methyltransferase that is essential for ribosome assembly and yeast viability [8].
• Likewise, nitrate uptake detected in the strain FM31 is independent of both Ynt1p and Yna1p and is not affected by ammonium, glutamine or chlorate [9].

Analytical, diagnostic and therapeutic context of NOP2

• Indirect immunofluorescence localization of Nop2p shows a nucleolar-staining pattern, which is heterogeneous in appearance, and a faint staining of the cytoplasm [2].
• A total of nine conserved residues, including Pro423 and Cys424, were individually altered in Nop2p by site-directed mutagenesis [7].

References