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''Bgl''II (pronounced "begel two") is a type II restriction endonuclease enzyme isolated from certain strains of ''Bacillus globigii''. The principal function of restriction enzymes is the protection of the host genome against foreign DNA, but they may also have some involvement in recombination and transposition. Like most type II restriction enzymes, ''Bgl''II consists of two identical subunits that form a homodimer around the DNA double helix. Each monomer is 223 amino acids and symmetrically bind both sides of the unique palindromic nucleotide sequence AGATCT, cleaving the scissile phosphodiester bond between the first Adenine and Guanine nucleotides on both strands of the DNA molecule, creating sticky ends with 5' end overhangs. Being a type II restriction enzyme, ''Bgl''II does not require ATP (adenosine triphosphate) for its enzymatic function, but only requires association with a divalent metal cation, most likely Mg2+. Unlike other restriction enzymes of its class, ''Bgl''II has been show to possess some unique structural characteristics, such as a β-sandwich subdomain, and appears to undergo a unique conformational change upon dimerization, but its overall structure and mechanism of catalysis remain consistent with other type II restriction enzymes. Restriction Endonuclease enzymes play a very important role in modern molecular cloning techniques. Because of their unique recognition/cut sites, restriction enzymes can be used to precisely and controlably cut DNA in specific locations. Once cut, scientist can then insert the desired DNA fragment possessing "sticky ends" into a circular DNA molecule, and ligate them together to create an engineered cloning vector. == Mechanism == ''Bgl''II catalyses phosphodiester bond cleavage at the DNA backbone through a phosphoryl transfer to water.〔 Studies on the mechanism of restriction enzymes have revealed several general features that seem to be true in almost all cases, although the actual mechanism for each enzyme is most likely some variation of this general mechanism. This mechanism requires a base to generate the hydroxide ion from water, which will act as the nucleophile and attack the phosphorus in the phosphodiester bond. Also required is a Lewis acid to stabilize the extra negative charge of the pentacoordinated transition state phosphorus, as well as a general acid or metal ion that stabilizes the leaving group (3’-O-). 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「BglII」の詳細全文を読む スポンサード リンク
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