Hohjoh H, Minakami R, Sakaki Y
Research Laboratory for Genetic Information, Kyushu University, Fukuoka, Japan.
Nucleic Acids Res. 1990 Jul 25;18(14):4099-104. doi: 10.1093/nar/18.14.4099.
L1 (LINE-1), a long interspersed repetitive DNA family of mammalian genomes, is thought to be a sequence family derived from a retrotransposon-like element(s), but its actively transposable unit(s) has not been identified yet. We developed a novel method for selective isolation of the human L1 sequences which transposed in a relatively recent past and may have still retained a feature of the 'active L1' unit. From the inspection of the nucleotide sequences, we conjectured that the 'active L1' or 'nearly active L1' units should have a high content of the CpG dinucleotide sequence, a mutation hot spot sequence, and contain several sites for rare cutters such as BssH II and Nar I at their 5' terminal regions. Using these rare cutter sites as selection markers, the L1 sequences were isolated, which had the high content of CpG at the 5' terminal regions and over 90% homology to L1 transcripts found in a human teratocarcinoma cell line. These L1s were shown to be 'relatively new L1' units which had integrated into chromosomes within these several million years during evolution. From the sequence data of these L1s and L1 cDNA, a consensus sequence of the 5' terminal region of high CpG L1s were constructed. A region of the consensus sequence showed about 69% homology to the 5' terminal region of Drosophila jockey element.
L1（长散布重复序列1）是哺乳动物基因组中的一个长散布重复DNA家族，被认为是一个源自类逆转座子元件的序列家族，但其活跃的转座单位尚未被确定。我们开发了一种新方法，用于选择性分离在相对较近时期发生转座且可能仍保留“活跃L1”单位特征的人类L1序列。通过对核苷酸序列的检查，我们推测“活跃L1”或“近乎活跃L1”单位应具有高含量的CpG二核苷酸序列（一种突变热点序列），并且在其5'末端区域包含几个稀有切割酶（如BssH II和Nar I）的切割位点。以这些稀有切割酶位点作为选择标记，分离出了在5'末端区域具有高含量CpG且与人类畸胎瘤细胞系中发现的L1转录本具有90%以上同源性的L1序列。这些L1被证明是在进化过程中数百万年内整合到染色体中的“相对较新的L1”单位。根据这些L1和L1 cDNA的序列数据，构建了高CpG L1的5'末端区域的共有序列。该共有序列的一个区域与果蝇jockey元件的5'末端区域显示出约69%的同源性。
