InterPro domain: IPR011023

This domain is found in archaeal, bacterial and eukaryotic proteins.

In the archaea and bacteria, they are primarily restricted to the euryarchaeota and proteobacteria respectively; where they are either described as either nucleolar protein or tRNA/rRNA cytosine-C5-methylase. They all have the S-adenosyl methionine (SAM) binding domain and are related to bacterial Fmu (16S rRNA m5C 967 methyltransferase) where the structure of the methyl transferase domain has been determined [ 1 ].

In the eukaryota, the majority are annotated as being 'nucleolar protein'. None of the eukaryotic members in this family have a the SAM binding signature. Despite this, the yeast Nop2p is a probable RNA m(5)C methyltransferase, essential for processing and maturation of 27S pre-rRNA and large ribosomal subunit biogenesis [ 2 ]; localised to the nucleolus and is essential for viability [ 3 ]. Reduced Nop2p expression limits yeast growth and decreases levels of mature 60S ribosomal subunits while altering rRNA processing [ 4 ]. There is substantial identity between Nop2p and human p120 (NOL1), which is also called the proliferation-associated nucleolar antigen [ 5 , 5 ].

1. The first structure of an RNA m5C methyltransferase, Fmu, provides insight into catalytic mechanism and specific binding of RNA substrate. Structure 11, 1609-20
2. Automated identification of putative methyltransferases from genomic open reading frames. Mol. Cell Proteomics 2, 525-40
3. Yeast NOP2 encodes an essential nucleolar protein with homology to a human proliferation marker. J. Cell Biol. 127, 1799-813
4. Nop2p is required for pre-rRNA processing and 60S ribosome subunit synthesis in yeast. Mol. Cell. Biol. 17, 378-88
5. Cloning of the cDNA and sequence of the human proliferating-cell nucleolar protein P120. Cancer Commun. 1, 243-51