Feng Q, Moran J V, Kazazian H H, Boeke J D
Department of Molecular Biology and Genetics, School of Medicine, Johns Hopkins University, Baltimore, Maryland 21205, USA.
Cell. 1996 Nov 29;87(5):905-16. doi: 10.1016/s0092-8674(00)81997-2.
Human L1 elements are highly abundant poly(A) (non-LTR) retrotransposons whose second open reading frame (ORF2) encodes a reverse transcriptase (RT). We have identified an endonuclease (EN) domain at the L1 ORF2 N-terminus that is highly conserved among poly(A) retrotransposons and resembles the apurinic/apyrimidinic (AP) endonucleases. Purified L1 EN protein (L1 ENp) makes 5'-PO4, 3'-OH nicks in supercoiled plasmids, shows no preference for AP sites, and preferentially cleaves sequences resembling L1 in vivo target sequences. Mutations in conserved amino acid residues of L1 EN abolish its nicking activity and eliminate L1 retrotransposition. We propose that L1 EN cleaves the target site for L1 insertion and primes reverse transcription.
人类L1元件是高度丰富的多聚腺苷酸（非LTR）逆转座子，其第二个开放阅读框（ORF2）编码逆转录酶（RT）。我们在L1 ORF2的N端鉴定出一个核酸内切酶（EN）结构域，该结构域在多聚腺苷酸逆转座子中高度保守，类似于脱嘌呤/脱嘧啶（AP）核酸内切酶。纯化的L1 EN蛋白（L1 ENp）在超螺旋质粒中产生5'-PO4、3'-OH切口，对AP位点无偏好，并优先切割体内靶序列中与L1相似的序列。L1 EN保守氨基酸残基的突变消除了其切口活性并消除了L1逆转座。我们提出L1 EN切割L1插入的靶位点并引发逆转录。
