Okada N
Institute of Biological Sciences, University of Tsukuba, Ibaraki, Japan.
J Mol Evol. 1990 Dec;31(6):500-10. doi: 10.1007/BF02102077.
Structural resemblance of the human Alu family with a subset of vertebrate tRNAs was detected. Of four tRNAs, tRNA(Lys), tRNA(Ile), tRNA(Thr), and tRNA(Tyr), which comprise a structurally related family, tRNA(Lys) is the most similar to the human Alu family. Of the 76 nucleotides in lysine tRNA (including the CCA tail), 47 are similar to the human Alu family (60% identity). The secondary structure of the human Alu family corresponding to the D-stem and anticodon stem regions of the tRNA appears to be very stable. The 7SL RNA, which is a progenitor of the human Alu family, is less similar to lysine tRNA (55% identity), and the secondary structure of the 7SL RNA folded like a tRNA is less stable than that of the human Alu family folded likewise. Insertion of the tetranucleotide GAGA, which is an important region of the second promoter for RNA polymerase III in the Alu sequence, occurred during the deletion and ligation process to generate the Alu sequence from the parental 7SL RNA. These results suggest that the human Alu family was generated from the 7SL RNA by deletion, insertion, and mutations, which thus modified the ancestral 7SL sequence so that it could form a structure more closely resembling lysine tRNA. The similarities of several short interspersed sequences to the lysine tRNA were also examined. The Galago type 2 family, which was reported to be derived from a methionine initiator tRNA, was also found to be similar to the lysine tRNA. Thus lysine tRNA-like structures are widespread in genomes in the animal kingdom. The implications of these findings in relation to the mechanism of generation of the human Alu family and its possible functions are discussed.
检测到人类Alu家族与脊椎动物tRNA的一个子集存在结构相似性。在构成一个结构相关家族的四种tRNA（tRNA(Lys)、tRNA(Ile)、tRNA(Thr)和tRNA(Tyr)）中，tRNA(Lys)与人类Alu家族最为相似。赖氨酸tRNA中的76个核苷酸（包括CCA尾），有47个与人类Alu家族相似（同一性为60%）。与tRNA的D茎和反密码子茎区域相对应的人类Alu家族二级结构似乎非常稳定。作为人类Alu家族祖源的7SL RNA与赖氨酸tRNA的相似性较低（同一性为55%），并且折叠成tRNA样的7SL RNA二级结构比同样折叠的人类Alu家族二级结构更不稳定。在从亲本7SL RNA产生Alu序列的缺失和连接过程中，发生了四核苷酸GAGA的插入，GAGA是Alu序列中RNA聚合酶III第二个启动子的重要区域。这些结果表明，人类Alu家族是通过缺失、插入和突变从7SL RNA产生的，从而修饰了祖先的7SL序列，使其能够形成更类似于赖氨酸tRNA的结构。还研究了几种短散在序列与赖氨酸tRNA的相似性。据报道源自甲硫氨酸起始tRNA的夜猴属2家族也被发现与赖氨酸tRNA相似。因此，赖氨酸tRNA样结构在动物界的基因组中广泛存在。讨论了这些发现与人类Alu家族产生机制及其可能功能的关系。
