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2'-O-Methylation

''2'-O-methylation is a common nucleoside modification of RNA, where a methyl group is added to the 2' hydroxyl group of the ribose moiety of a nucleoside. 2'-O-methylated nucleosides are mostly found in ribosomal RNA and small nuclear RNA and occur in the functionally essential regions of the ribosome and splicesome. Also, 2'-O-methylation of adenosine in an RNA prevents adenosine deaminase from editing it to an inosine.''

Recently a novel method to map 2'-O ribose methylations by high throughput sequencing has been published. The method is quantitative and maps all modifications in a single experiment.

Functions
In general, 2'-O-methylation is a common post-transcriptional modification of naturally occurring stable RNAs.

tRNAs
2'-O-methylation only occurs at certain positions (e.g. on first nucleotide of tRNA1-Ser's anticodon) to stabilize the codon-anticodon duplex, and in vitro experiments indicate that at other locations (e.g. on second or third nucleotide of tRNA1-Ser's anticodon) 2'-O-methylation disrupts codon-reading activity. Anticodon of eucaryotic tRNA-Phe has 2'-O-methylated cytidine and guanosine at positions 32 and 34, which are involved in frameshift maintenance. A recent study also links defective 2'-O-methylation at these two locations to loss-of-function of FTSJ1 gene, which causes nonsyndromic X-linked intellectual disability.

mRNAs
Many eukaryotes have their mRNAs 2'-O-methylated at 5' cap, but their function remains largely unknown. Certain viruses that operate in eukaryotes have also evolved with 2'-O-methylation at 5' cap which allows them to evade innate host immune responses. Usually detectors in cytosol, such as Mda5, initiate the signaling cascades if viral RNA is present, and interferons, a group of signaling proteins, notify neighbouring cells. Viruses with 2'-O-methylation at 5' cap, such as West Nile viruses, have a much smaller chance of inducing high interferon expression, which suggests 2'-O-methylation is a mechanism involved in distinguishing between self and non-self (e.g. viral) mRNAs.

rRNAs
2'-O-methylation is an indispensable step in ribosome biogenesis. With the help of snoRNAs, whose roles are guides for the 2'-O-methylation of rRNAs, rRNA precursor can be cleaved to become subunits, and to be exported from nucleus to cytoplasm for ribosome assembly.

miRNAs
A miRNA is a small non-coding RNA molecule that acts as RNA silencer. Plant miRNAs undergo 3'-end 2'-O-methylation, which is essential for their maturation and stability. In Drosophila, a genus of flies, positive correlation between age and 2'-O-methylation has been found.

piRNAs
In animals, piRNAs, small non-coding RNA molecules slightly larger than miRNAs, are 2'-O-methylated at 3' end as a tag to stop further nucleotide addition and to stabilize themselves.