Zimmerly S, Guo H, Perlman P S, Lambowitz A M
Department of Molecular Genetics, Ohio State University, Columbus 43210-1292, USA.
Cell. 1995 Aug 25;82(4):545-54. doi: 10.1016/0092-8674(95)90027-6.
Mobile group II introns encode reverse transcriptases and insert site specifically into intronless alleles (homing). Here, in vitro experiments show that homing of the yeast mtDNA group II intron aI2 occurs by reverse transcription at a double-strand break in the recipient DNA. A site-specific endonuclease cleaves the antisense strand of recipient DNA at position +10 of exon 3 and the sense strand at the intron insertion site. Reverse transcription of aI2-containing pre-mRNA is primed by the antisense strand cleaved in exon 3 and results in cotransfer of the intron and flanking exon sequences. Remarkably, the DNA endonuclease that initiates homing requires both the aI2 reverse transcriptase protein and aI2 RNA. Parallels in their reverse transcription mechanisms raise the possibility that mobile group II introns were ancestors of nuclear non-long terminal repeat retrotransposons and telomerases.
移动性II类内含子编码逆转录酶，并特异性地插入无内含子的等位基因中（归巢）。在此，体外实验表明，酵母线粒体DNA的II类内含子aI2通过在受体DNA的双链断裂处进行逆转录来实现归巢。一种位点特异性内切核酸酶在第3外显子的+10位置切割受体DNA的反义链，并在内含子插入位点切割有义链。含aI2的前体mRNA的逆转录由在第3外显子中切割的反义链引发，并导致内含子和侧翼外显子序列的共转移。值得注意的是，启动归巢的DNA内切核酸酶需要aI2逆转录酶蛋白和aI2 RNA。它们逆转录机制的相似性增加了移动性II类内含子是核非长末端重复逆转座子和端粒酶祖先的可能性。
