Edlind T D, Sharetzsky C, Cha M E
Department of Microbiology and Immunology, Medical College of Pennsylvania, Philadelphia 19129.
Gene. 1990 Dec 15;96(2):289-93. doi: 10.1016/0378-1119(90)90266-t.
The cytoplasmic ribosomal RNA (rRNA) from the intestinal protozoan, Giardia lamblia, is unusually short; the large subunit (LS) and small subunit RNA and the 5.8S RNA are only 70-80% of the length found in typical protozoa, and are even smaller than most of their prokaryotic counterparts. Flanking regulatory DNA and processed rRNA sequences are similarly compact in size. To shed light on the origins and implications of this 'minimal' rRNA, the nucleotide sequence encoding the 5.8S RNA and domain I of LS RNA was determined. Secondary structure analysis revealed that an evolutionarily variable internal hairpin is partially 'deleted' in G. lamblia 5.8S RNA; the 3'-terminal pairing with LS RNA is conserved. Previously characterized eukaryotic 'expansion' regions are extensively shortened within the LS RNA; in one case, a hairpin is precisely 'deleted'. The short sequences flanking the mature 5.8S RNA that are removed by RNA processing (ITS1 and ITS2) are C-rich; our analysis suggests that the sequence GCGCCCC, in a hairpin configuration, may function as the processing signal.
肠道原生动物蓝氏贾第鞭毛虫的细胞质核糖体RNA（rRNA）异常短小；大亚基（LS）、小亚基RNA以及5.8S RNA的长度仅为典型原生动物中相应RNA长度的70%-80%，甚至比大多数原核生物的对应RNA还要小。侧翼调控DNA和加工后的rRNA序列在大小上同样紧凑。为了阐明这种“最小化”rRNA的起源及影响，我们测定了编码5.8S RNA和LS RNA结构域I的核苷酸序列。二级结构分析表明，在蓝氏贾第鞭毛虫5.8S RNA中，一个进化上可变的内部发夹结构部分“缺失”；其与LS RNA的3'末端配对是保守的。先前已鉴定的真核生物“扩展”区域在LS RNA中大幅缩短；在一种情况下，一个发夹结构精确“缺失”。通过RNA加工去除的成熟5.8S RNA侧翼的短序列富含C；我们的分析表明，呈发夹结构的序列GCGCCCC可能作为加工信号。
