Sloof P, Van den Burg J, Voogd A, Benne R, Agostinelli M, Borst P, Gutell R, Noller H
Nucleic Acids Res. 1985 Jun 11;13(11):4171-90. doi: 10.1093/nar/13.11.4171.
We have determined the nucleotide sequence of a maxi-circle segment from the insect trypanosome Crithidia fasciculata mitochondrial DNA, on which the genes for the major maxicircle transcripts of 9S and 12S are localized. The 5'-terminal sequences of these RNAs were determined by wandering spot analysis. The map coordinates of the 9S and 12S RNAs from Trypanosoma brucei were adjusted with respect to a previous report with the aid of primer extension analysis with reverse transcriptase. This approach allowed us to align the corresponding genes from both organisms which show an overall sequence homology of 77%. The 9S and 12S RNA genes from the two trypanosome species contain sequences, closely related to some of the regions that are universally conserved among ribosomal RNAs from members of the three primary kingdoms and their organelles, even though the overall level of sequence homology is extremely low. These universal sequences occur at positions in the 9S and 12S RNAs that are analogous to those occupied by their counterparts in authentic ribosomal RNAs. The characteristic secondary structure elements flanking these universal sequences in genuine ribosomal RNAs can also be formed in the trypanosomal 9S and 12S RNAs. These results provide unequivocal evidence for a ribosomal function of the 9S and 12S RNAs of trypanosomal mitochondria, notwithstanding their extremely small size (estimated to be 612 and 1141 nucleotides in C. fasciculata, 611 and 1150 nucleotides in T. brucei) and their unusual base composition (83% A+U).
我们已经确定了昆虫锥虫克氏锥虫线粒体DNA中一个大圆环片段的核苷酸序列，9S和12S主要大圆环转录本的基因就定位在该片段上。通过漫游斑点分析确定了这些RNA的5'-末端序列。借助逆转录酶的引物延伸分析，对来自布氏锥虫的9S和12S RNA的图谱坐标进行了调整，使其与之前的一份报告一致。这种方法使我们能够比对这两种生物的相应基因，它们的整体序列同源性为77%。这两种锥虫物种的9S和12S RNA基因包含一些序列，这些序列与三个主要界及其细胞器的核糖体RNA中普遍保守的某些区域密切相关，尽管序列同源性的总体水平极低。这些通用序列出现在9S和12S RNA中的位置，类似于它们在真正的核糖体RNA中的对应序列所占据的位置。在真正的核糖体RNA中，这些通用序列两侧的特征性二级结构元件在锥虫的9S和12S RNA中也能形成。这些结果为锥虫线粒体的9S和12S RNA具有核糖体功能提供了明确的证据，尽管它们的尺寸极小（在克氏锥虫中估计为612和1141个核苷酸，在布氏锥虫中为611和1150个核苷酸），且碱基组成异常（83%为A+U）。
