RNA modifications (synthesis of 5 prime cap)

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In molecular biology, the 5′ cap is a specially altered nucleotide on the 5′ end of precursor messenger RNA and some other primary RNA transcripts as found in eukaryotes. 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 that occurs in the cell nucleus. Because this only occurs in the nucleus, mitochondrial and chloroplast mRNA are not capped.
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 vivo by a methyl transferase. It is referred to as a 7-methylguanylate cap, abbreviated m7G. Further modifications include the possible methylation of the 2′ hydroxy-groups of the first 2 ribose sugars of the 5′ end of the mRNA. The methylation of both 2′ hydroxy-groups is shown on the diagram. The 5′ cap looks like the 3′ end of an RNA molecule (the 5′ carbon of the cap ribose is bonded, and the 3′ unbonded). This provides significant resistance to 5′ exonucleases.
The starting point is the unaltered 5′ end of an RNA molecule. This features a final nucleotide followed by three phosphate groups attached to the 5′ carbon.

One of the terminal phosphate groups is removed (by RNA terminal phosphatase), leaving two terminal phosphates.
GMP is added to the terminal phosphates (by a guanylyl transferase), losing two phosphate groups (from the GTP substrate) in the process. This results in the 5′--5′ triphosphate linkage.
The 7-nitrogen of guanine is methylated (by a methyl transferase).
If the second base from the terminal is adenine, it can be methylated; and the third base from the terminal is generally methylated 10--15% of the time. Source of the article published in description is Wikipedia. I am sharing their material. Copyright by original content developers of Wikipedia.
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