Methylated RNA

Methylated RNA

Small nucleolar RNAs (snoRNAs) are a class of small RNA molecules that guide chemical modifications (methylation or pseudouridylation) of ribosomal RNAs (rRNAs) and other RNA genes (tRNAs and other small nuclear RNAs (snRNAs). They are classified under snRNA in MeSH. snoRNAs are commonly referred to as guide RNAs but should not be confused with the guide RNAs (gRNA) that direct RNA editing in trypanosomes.

5' cap

The 5' cap is a specially altered nucleotide end to the 5' end of precursor messenger RNA and some other primary RNA transcripts as found in eukaryotes and, as a special exception, caliciviruses, of which norovirus is one. The process of 5' capping is vital to creating mature messenger RNA which is then able to undergo translation. Capping ensures the messenger RNA's stability while it undergoes translation in the process of protein synthesis, and is a highly regulated process which occurs in the cell nucleus.

5' cap Structure

The 5' cap is found on the 5' end of an mRNA molecule and consists of a guanine nucleotide connected to the mRNA via an unusual 5' to 5' triphosphate linkage. This guanosine is methylated on the 7 position directly after capping in vitro by a methyl transferase. It is referred to as a 7-methylguanosine cap, abbreviated m7G.

SnoRNA Guided Modifications

After transcription, nascent rRNA molecules (termed pre-rRNA) are required to undergo a series of processing steps in order to generate the mature rRNA molecule. Prior to cleavage by exo- and endonucleases the pre-rRNA undergoes a complex pattern of nucleoside modifications. These include methylations and pseudouridylations, guided by snoRNAs. Methylation is the attachment or substitution of a methyl group onto various substrates.