Kapitonov Vladimir V, Jurka Jerzy
Genetic Information Research Institute, Mountain View, California, USA.
Mol Biol Evol. 2003 May;20(5):694-702. doi: 10.1093/molbev/msg075. Epub 2003 Apr 2.
Eukaryotic genomes are colonized by different retroposons, including short interspersed repetitive elements (SINEs). All currently known SINEs are derived from tRNA and 7SL RNA genes and exploit their type 2 internal pol III promoters. We report here a novel class of SINE elements, called SINE3, derived from 5S rRNA. SINE3s are transcribed from the type 1 internal pol III promoter. Approximately 10,000 copies of SINE3 elements are present in the zebrafish genome, they constitute approximately 0.4% of the genomic DNA. Some elements are as little as 1% diverged from each other, indicating that the retrotransposition of SINE3 in zebrafish is an ongoing process. The 3'-tail of SINE3 is significantly similar to that of CR1-like non-LTR retrotransposons, represented by numerous subfamilies in the zebrafish genome. Analogously to CR1-like elements, SINE3 copies are not flanked by target site duplications, and their 3' termini are composed of (ACATT)n and (ATT)n microsatellites, specific for different subfamilies of SINE3. Given the common structural features, it is highly likely that the enzymatic machinery encoded by CR1-like elements powers proliferation of SINE3.
真核生物基因组被不同的逆转座子所占据，包括短散在重复元件（SINEs）。目前已知的所有SINEs都来源于tRNA和7SL RNA基因，并利用它们的2型内部RNA聚合酶III启动子。我们在此报告了一类新的SINE元件，称为SINE3，它来源于5S rRNA。SINE3由1型内部RNA聚合酶III启动子转录。斑马鱼基因组中存在约10000个SINE3元件拷贝，它们约占基因组DNA的0.4%。一些元件彼此之间的差异小至1%，这表明SINE3在斑马鱼中的逆转座是一个持续进行的过程。SINE3的3'末端与CR1样非LTR逆转座子的3'末端显著相似，斑马鱼基因组中有许多亚家族代表了CR1样非LTR逆转座子。与CR1样元件类似，SINE3拷贝的两侧没有靶位点重复，并且它们的3'末端由（ACATT）n和（ATT）n微卫星组成，这些微卫星对SINE3的不同亚家族具有特异性。鉴于共同的结构特征，极有可能是由CR1样元件编码的酶促机制推动了SINE3的增殖。
