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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Protospacer adjacent motif ： ウィキペディア英語版 Protospacer adjacent motif Protospacer adjacent motif (PAM) is a DNA sequence immediately following the DNA sequence targeted by the Cas9 nuclease in the CRISPR bacterial adaptive immune system. PAM is a component of the invading virus or plasmid, but is not a component of the bacterial CRISPR locus. Cas9 will not successfully bind to or cleave the target DNA sequence if it is not followed by the PAM sequence. PAM is an essential targeting component (not found in bacteria) which distinguishes bacterial self from non-self DNA, thereby preventing the CRISPR locus from being targeted and destroyed by nuclease. CRISPR loci in a bacterium contain "spacers" (viral DNA inserted into a CRISPR locus) that in type II adaptive immune systems were created from invading viral or plasmid DNA (called "protospacers"). On subsequent invasion, Cas9 nuclease attaches to tracrRNA:crRNA which guides Cas9 to the invading protospacer sequence. But Cas9 will not cleave the protospacer sequence unless there is an adjacent PAM sequence. The spacer in the bacterial CRISPR loci will not contain a PAM sequence, and will thus not be cut by the nuclease. But the protospacer in the invading virus or plasmid will contain the PAM sequence, and will thus be cleaved by the Cas9 nuclease.〔 For editing genes, guideRNAs (gRNAs) are synthesized to perform the function of the tracrRNA:crRNA complex in recognizing gene sequences having a PAM sequence at the 3'-end. The canonical PAM is the sequence 5'-NGG-3' where "N" is any nucleobase followed by two guanine ("G") nucleobases. Guide RNAs (gRNAs) can transport Cas9 to anywhere in the genome for gene editing, but no editing can occur at any site other than one at which Cas9 recognizes PAM. The canonical PAM is associated with the Cas9 nuclease of Streptococcus pyogenes (designated SpCas9), whereas different PAMs are associated with the Cas9 proteins of the bacteria Neisseria meningitidis, Treponema denticola, and Streptococcus thermophilus. 5'-NGA-3' can be a highly efficient non-canonical PAM for human cells, but efficiency varies with genome location. Attempts have been made to engineer Cas9s to recognize different PAMs to improve ability of CRISPR-Cas9 to do gene editing at any desired genome location. A technology called GUIDE-Seq has been devised to assay off-target cleavages produced by such gene editing. ==See also== * CRISPR 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「Protospacer adjacent motif」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.