Alternative titles; symbols
HGNC Approved Gene Symbol: RNMT
Cytogenetic location: 18p11.21 Genomic coordinates (GRCh38) : 18:13,726,673-13,764,556 (from NCBI)
In mammals, 5-prime-terminal caps are formed on nascent pre-mRNAs by the sequential action of 2 enzymes, the bifunctional capping enzyme RNGTT (603512) and RNA guanine-7-methyltransferase (RNMT). RNGTT catalyzes the removal of the gamma-phosphate of the initiating nucleotide and transfers GMP from GTP to the resulting diphosphate end. RNMT catalyzes the subsequent N7 methylation of the newly formed termini. The terminal 7-methylguanosine is recognized by cap-binding proteins that facilitate key events in gene expression (summary by Pillutla et al., 1998).
By searching an EST database for sequences homologous to that of S. cerevisiae RNA guanine-7-methyltransferase, Pillutla et al. (1998) identified a human cDNA encoding RNMT, which they called MET. The predicted 476-amino acid MET protein contains several conserved motifs known to be required for methyltransferase activity.
By screening human brain cDNAs for those encoding large proteins, Ishikawa et al. (1997) identified KIAA0398, an RNMT cDNA.
Tsukamoto et al. (1998) isolated 3 human cDNAs encoding RNMT, which they termed HCMT1a, HCMT1b, and HCMT1c, which appear to be produced by alternative splicing. HCMT1a and HCMT1b encode deduced proteins of 476 and 504 amino acids, respectively, and differ only in the region encoding the C-terminal portion of the enzyme after residue 465. HCMT1c appears to encode the same polypeptide as HCMT1a; however, the 3-prime noncoding region of HCMT1c contains sequences corresponding to portions of both HCMT1a and HCMT1b. RT-PCR detected expression of the 3 mRNAs in all tissues tested.
Pillutla et al. (1998) found that recombinant human MET exhibited RNA guanine-7-methyltransferase activity in vitro and formed ternary complexes with RNGTT and the elongating form of RNA polymerase II.
Tsukamoto et al. (1998) showed that recombinant human HCMT1a expressed in E. coli exhibited mRNA RNMT activity, whereas recombinant HCMT1b did not.
Using immunoprecipitation analysis, Gonatopoulos-Pournatzis et al. (2011) found that RAM (FAM103A1; 614547) interacted with RNMT1 in several human cell lines. Gel filtration of HeLa cell extracts detected RAM and RNMT in a high molecular mass complex of about 200 kD. No RAM or RNMT monomers were detected. RNA band-shift assays showed that RAM, but not RNMT, interacted with RNA rather than the cap structure. Thin layer chromatography and quantitative phosphoimaging showed that recombinant RNMT, but not RAM, catalyzed methylation of the cap in a dose-dependent manner. Addition of RAM increased the cap methyltransferase activity of RNMT, and equimolar concentrations of RAM and RNMT resulted in highest cap methyltransferase activity. Mutation analysis revealed that amino acids 1 to 55 of RAM interacted with the methyltransferase domain of RNMT and were sufficient to activate RNMT-dependent cap methylation. The asn- and arg-rich region of RAM (amino acids 56 to 90) bound RNA. Knockdown of RAM in HeLa cells via small interfering RNA resulted in loss of RNMT expression and loss of cap methyltransferase activity. Knockdown of RAM also caused loss of polysomes and reduced protein synthesis, consistent with loss of mRNA translation. Knockdown of RNMT caused loss of RAM expression, suggesting that the 2 proteins stabilize each other. Gonatopoulos-Pournatzis et al. (2011) concluded that RAM is essential for RNMT cap methyltransferase activity.
By analysis of a radiation hybrid panel, Pillutla et al. (1998) and Ishikawa et al. (1997) mapped the RNMT gene to chromosome 18. Pillutla et al. (1998) refined the location to 18p11.23-p11.22 using fluorescence in situ hybridization.
Gonatopoulos-Pournatzis, T., Dunn, S., Bounds, R., Cowling, V. H. RAM/Fam103a1 is required for mRNA cap methylation. Molec. Cell 44: 585-596, 2011. [PubMed: 22099306] [Full Text: https://doi.org/10.1016/j.molcel.2011.08.041]
Ishikawa, K., Nagase, T., Nakajima, D., Seki, N., Ohira, M., Miyajima, N., Tanaka, A., Kotani, H., Nomura, N., Ohara, O. Prediction of the coding sequences of unidentified human genes. VIII. 78 new cDNA clones from brain which code for large proteins in vitro. DNA Res. 4: 307-313, 1997. [PubMed: 9455477] [Full Text: https://doi.org/10.1093/dnares/4.5.307]
Pillutla, R. C., Shimamoto, A., Furuichi, Y., Shatkin, A. J. Human mRNA capping enzyme (RNGTT) and cap methyltransferase (RNMT) map to 6q16 and 18p11.22-p11.23, respectively. Genomics 54: 351-353, 1998. [PubMed: 9828141] [Full Text: https://doi.org/10.1006/geno.1998.5604]
Pillutla, R. C., Yue, Z., Maldonado, E., Shatkin, A. J. Recombinant human mRNA cap methyltransferase binds capping enzyme/RNA polymerase IIo complexes. J. Biol. Chem. 273: 21443-21446, 1998. [PubMed: 9705270] [Full Text: https://doi.org/10.1074/jbc.273.34.21443]
Tsukamoto, T., Shibagaki, Y., Niikura, Y., Mizumoto, K. Cloning and characterization of three human cDNAs encoding mRNA (guanine-7)-methyltransferase, an mRNA cap methylase. Biochem. Biophys. Res. Commun. 251: 27-34, 1998. [PubMed: 9790902] [Full Text: https://doi.org/10.1006/bbrc.1998.9402]