Lykke-Andersen J, Garrett R A
Institute of Molecular Biology, Copenhagen University, Denmark.
J Mol Biol. 1994 Nov 11;243(5):846-55. doi: 10.1006/jmbi.1994.1687.
Five pre-23 S rRNA introns have been characterized for hyperthermophilic archaea. The small ones constitute stable core structures while the three larger ones contain, in addition, open reading frames, two of which encode homing-type endonucleases. The higher order structures of in vitro transcripts of the introns and their exon-intron junctions were examined using chemical and ribonuclease probes specific for unpaired nucleotides, double helical regions and helix-loop junctions. The experimental data support both the formation of a "bulge-helix-bulge" structural motif at the exon-intron junctions, which is recognized by a cleavage enzyme, and the presence of an adjacent core structure consisting of a long, stable, stem-loop structure. Moreover, the data were used to derive secondary structural models for the three large introns which form stable, circular, RNA species, in vivo. Each exhibits extensive secondary structure and additional, as yet undefined, higher order structure, compatible with their high level of stability in vivo; limited structural similarities were detected between the two introns encoding the homing-type endonucleases. The data are compatible with the hypothesis that RNA introns can be transmitted between archaeal hyperthermophile cells.
已对嗜热古菌的5个23 S rRNA前体内含子进行了表征。较小的内含子构成稳定的核心结构，而三个较大的内含子还含有开放阅读框，其中两个编码归巢型内切核酸酶。使用对未配对核苷酸、双螺旋区域和螺旋-环连接点具有特异性的化学和核糖核酸酶探针，研究了内含子及其外显子-内含子连接点的体外转录本的高级结构。实验数据支持在外显子-内含子连接点形成一种“凸起-螺旋-凸起”结构基序（可被一种切割酶识别），以及存在一个由长的、稳定的茎环结构组成的相邻核心结构。此外，这些数据被用于推导三个大型内含子的二级结构模型，这些内含子在体内形成稳定的环状RNA分子。每个内含子都具有广泛的二级结构以及额外的、尚未明确的高级结构，这与其在体内的高稳定性相一致；在编码归巢型内切核酸酶的两个内含子之间检测到有限的结构相似性。这些数据与RNA内含子可在嗜热古菌细胞之间传递的假说相符。
