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|Section2= |Section3= }} 5-Methylcytosine is a methylated form of the DNA base cytosine that may be involved in the regulation of gene transcription. When cytosine is methylated, the DNA maintains the same sequence, but the expression of methylated genes can be altered (the study of this is part of the field of epigenetics). 5-Methylcytosine is incorporated in the nucleoside 5-methylcytidine. In 5-methylcytosine, a methyl group is attached to the 5th atom in the 6-atom ring (counting counterclockwise from the NH nitrogen at the six o'clock position, not the 2 o'clock). This methyl group distinguishes 5-methylcytosine from cytosine. ==Discovery== While trying to isolate the bacterial toxin responsible for tuberculosis, W.G. Ruppel isolated a novel nucleic acid named tuberculinic acid in 1898 from ''Tubercle bacillus''. The nucleic acid was found to be unusual, in that it contained in addition to thymine, guanine and cytosine, a methylated nucleotide. In 1925, Johnson and Coghill successfully detected a minor amount of a methylated cytosine derivative as a product of hydrolysis of tuberculinic acid with sulfuric acid.〔Grosjean H (2009). (Nucleic Acids Are Not Boring Long Polymers of Only Four Types of Nucleotides: A Guided Tour ). Landes Bioscience.〕 This report was severely criticized because their identification based solely on the optical properties of the crystalline picrate, and other scientists failed to reproduce the same result. But the existence was ultimately proved a fact in 1948, when Hotchkiss separated the nucleic acids of DNA from calf thymus using paper chromatography, by which he detected a unique methylated cytosine, quite distinct from conventional cytosine and uracil. After seven decades, it turned out that it is also a common feature in different RNA molecules, although the precise role is uncertain. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「5-Methylcytosine」の詳細全文を読む スポンサード リンク
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