Sandbox Reserved 962: Difference between revisions
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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 capping. 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. | 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 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. | ||
The capping is therefore an important step of the maturation. It consists in adding a 7-methylguanosine on the first nucleotide of the mRNA with a diphosphate bonding. | The capping is therefore an important step of the maturation. It consists in adding a 7-methylguanosine on the first nucleotide of the mRNA with a diphosphate bonding. | ||
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. | 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}} | 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}} | ||
[[Image:Cap.png]][[Image:Step_cap.png]] {{clear}} | |||
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The structure of ECM1 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 | We can indentify structural repeatings characteristic of the family : amongst others alpha helices or beta-sheets can be found. | ||
The structure of the protein could be divided in two segments : | The structure of the protein could be divided in two segments : | ||
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• The <scene name='60/604481/Segment_1/1'>first segment</scene> from the aminoacids 41 to 62 and from 165 to 292 : carrys the <scene name='60/604481/Helices_segment_1/1'>alpha helices A, F, H, E, I and G</scene>. The helices G, H and I are the <scene name='60/604481/Helices_c_terminal/1'>C-terminal helices</scene> from the aminoacid 249 to 284. This segment carrys also the <scene name='60/604481/Sheets_segment_1/1'>bêta-sheets from 5 to 11</scene>. | • The <scene name='60/604481/Segment_1/1'>first segment</scene> from the aminoacids 41 to 62 and from 165 to 292 : carrys the <scene name='60/604481/Helices_segment_1/1'>alpha helices A, F, H, E, I and G</scene>. The helices G, H and I are the <scene name='60/604481/Helices_c_terminal/1'>C-terminal helices</scene> from the aminoacid 249 to 284. This segment carrys also the <scene name='60/604481/Sheets_segment_1/1'>bêta-sheets from 5 to 11</scene>. | ||
• The <scene name='60/604481/Segment_2/1'>second segment</scene> from the aminoacids 63 to 164 : carrys the <scene name='60/604481/Helices_segment_2/1'>alpha helices B, C, D</scene> and the <scene name='60/604481/Sheets_segment_2/1'> | • The <scene name='60/604481/Segment_2/1'>second segment</scene> from the aminoacids 63 to 164 : carrys the <scene name='60/604481/Helices_segment_2/1'>alpha helices B, C, D</scene> and the <scene name='60/604481/Sheets_segment_2/1'>beta-sheets from 1 to 4</scene>. <ref name="Fabrega C, Hausmann S, Shen V, Shuman S, Lima CD. Structure and mechanism of mRNA cap (guanine-N7) methyltransferase. Mol Cell. 2004 Jan 16;13(1):77-89. ">PMID:14731396</ref> | ||
