Sandbox Reserved 962: Difference between revisions

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'''mRNA Cap (Guanine-N7) Methyltransferase (Ecm1)'''  
'''mRNA Cap (Guanine-N7) Methyltransferase (Ecm1)'''  


The mRNA Cap (Guanine-N7) Methyltransferase is an enzyme which catalyses the reaction of capping the C-terminal domain of a mRNA with a m7G(5')pppR cap.
The mRNA Cap (Guanine-N7) Methyltransferase is involved in the capping of mRNA. This enzyme catalyses the methyl transfer reaction on the G(5')pppR cap at the C-terminal domain of a mRNA.
It has been the least understood enzyme intervening in capping. To be studied, the cap methyltransferase has been isolated on purified vaccinia virus by Martin and Moss in 1975-1976.
Ecm1 was isolated of Encephalitozoon cuniculi. This organism belongs to the phylum Microsporidia, in the kingdom of Fungi. E. cuniculi is an obligate intracellular parasite which is able to infect many mammals. An other particularity of this organism is that it had one of the smallest eukaryotic genome. Ecm1 is also the smallest cap methyltranferase identified.
 


<Structure load='1ri1' size='350' frame='true' align='right' caption='Ecm1' scene='60/604481/Scene_depart/3' />
<Structure load='1ri1' size='350' frame='true' align='right' caption='Ecm1' scene='60/604481/Scene_depart/3' />
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== Biological role==
== Biological role==


In eukaryotic cells the synthezise of mRNA is followed by a process of maturation. The best-known modifications are the polyadenylation, the splicing and the (Guanine-N7) capping. The capping is an important step of the maturation. It consists in adding a 7-methylguanosine on the first nucleotide of the mRNA with a diphosphate bonding.  
In eukaryotic cells, the synthezise of mRNA is followed by a process of maturation. The best-known modifications are the polyadenylation, the splicing and the capping. The capping is an important step of the maturation. It consists in adding a 7-methylguanosine on the first nucleotide of the mRNA with a diphosphate bonding.  
One of the enzymes catalysing this reaction is the mRNA Cap (Guanine-N7) Methyltransferase.  
The capping involved many steps: First the γ-phosphate from the 5′ end of the nascent RNA is removed.  Then a GMP is transfered from GTP to the 5′-diphosphate creating the guanosine 5′-5′-triphosphate. After that, a methyl group is transfered from S-adenosylmethionine to the N7 position of the guanine and an other is transfered to 2′ oxygen of riboses at the 5′ end of the mRNA.
Ecm1 catalyses the transfer of the methyl group  from S-adenosylmethionine to the N7 position of the guanine. This enzyme is a key enzyme in this capping process. {{clear}}


The cap allows the mRNA to be recognized by a protein complex which is involved in traduction initiation. It is also necessary to keep the stability of the mRNA.
The cap is important to the traduction initiation ; it allows the mRNA to be recognized by initiation factors. It is also necessary to keep the stability of the mRNA.


== Structure ==
== Structure ==
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This protein measures 292 aminoacids in lenght.  
This protein measures 292 aminoacids in lenght.  


The structure of ECM1 (the smallest cap methyltranferase identified) is similar to the structure of the whole family of cap methyltransferase.  
The structure of ECM1 is similar to the structure of the whole family of cap methyltransferase.  
We can indentify structural repeatings characteristic of the family : amongst others alpha helices or bêta-sheets can be found.  
We can indentify structural repeatings characteristic of the family : amongst others alpha helices or bêta-sheets can be found.  


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