共查询到10条相似文献,搜索用时 218 毫秒
1.
Most pseudouridinylation in eukaryotic rRNA and small nuclear RNAs is guided by H/ACA small nucleolar RNAs. In this study, the Trypanosoma brucei pseudouridine synthase, Cbf5p, a snoRNP protein, was identified and silenced by RNAi. Depletion of this protein destabilized all small nucleolar RNAs of the H/ACA-like family. Following silencing, defects in rRNA processing, such as accumulation of precursors and inhibition of cleavages to generate the mature rRNA, were observed. snR30, an H/ACA RNA involved in rRNA maturation, was identified based on prototypical conserved domains characteristic of this RNA in other eukaryotes. The silencing of CBF5 also eliminated the spliced leader-associated (SLA1) RNA that directs pseudouridylation on the spliced leader RNA (SL RNA), which is the substrate for the trans-splicing reaction. Surprisingly, the depletion of Cbf5p not only eliminated the pseudouridine on the SL RNA but also abolished capping at the fourth cap-4 nucleotide. As a result of defects in the SL RNA and decreased modification on the U small nuclear RNA, trans-splicing was inhibited at the first step of the reaction, providing evidence for the essential role of H/ACA RNAs and the modifications they guide on trans-splicing. 相似文献
2.
Different expression strategy: multiple intronic gene clusters of box H/ACA snoRNA in Drosophila melanogaster 总被引:4,自引:0,他引:4
The high degree of rRNA pseudouridylation in Drosophila melanogaster provides a good model for studying the genomic organization, structural and functional diversity of box H/ACA small nucleolar RNAs (snoRNAs). Accounting for both conserved sequence motifs and secondary structures, we have developed a computer-assisted method for box H/ACA snoRNA searching. Ten snoRNA clusters containing 42 box H/ACA snoRNAs were identified from D.melanogaster. Strikingly, they are located in the introns of eight protein-coding genes. In contrast to the mode of one snoRNA per intron so far observed in all animals, our results demonstrate for the first time a novel polycistronic organization that implies a different expression strategy for a box H/ACA snoRNA gene when compared to box C/D snoRNAs in D.melanogaster. Mutiple isoforms of the box H/ACA snoRNAs, from which most clusters are made up, were observed in D.melanogaster. The degree of sequence similarity between the isoforms varies from 99% to 70%, implying duplication events in different periods and a trend of enlarging the intronic snoRNA clusters. The variation in the functional elements of the isoforms could lead to partial alternation of snoRNA's function in loss or gain of rRNA complementary sequences and probably contributes to the great diversity of rRNA pseudouridylation in D.melanogaster. 相似文献
3.
snoRNA的结构与功能 总被引:1,自引:0,他引:1
核仁小分子RNA(snoRNA)是一类广泛分布于真核生物细胞核仁的小分子非编码RNA,具有保守的结构元件,并以此划分为3大类:boxC/DsnoRNA、boxH/ACAsnoRNA和MRPRNA。其中boxC/D和boxH/ACA是已知snoRNA的主要类型,以碱基配对的方式分别指导着核糖体RNA的甲基化和假尿嘧啶化修饰。研究发现,snoRNA除了在核糖体RNA的生物合成中发挥作用之外,还能够指导snRNA、tRNA和mRNA的转录后修饰。此外,还有相当数量的snoRNA功能不明,被称为孤儿sn0RNA(orphansnoRNA)。在哺乳动物的孤儿snoRNA中,印迹snoRNA(imprintedsnoRNA)是最为特殊的一群,由基因组印迹区编码,具有明显的组织表达特异性。原核生物古细菌中类snoRNA的鉴定表明这些非编码RNA家族成员的古老起源;而哺乳动物中大量的snoRNA反转座子的存在更为人们探索snoRNA在基因组中扩增和功能进化提供了新的思路。 相似文献
4.
Liang XH Ochaion A Xu YX Liu Q Michaeli S 《The Journal of biological chemistry》2004,279(7):5100-5109
5.
最新研究结果表明,一些与RNA介导基因沉默相关的小RNA由核仁小RNA(small nucleolar RNA,snoRNA)加工产生,这种小RNA被称为核仁小RNA源性小RNA(snoRNA derived small RNA,sdRNA)。sdRNA现象分布物种广;涉及的snoRNA种类全,数量多;产生的小RNA分子大小不一、数量、种类多。表明这种小RNA在生物中存在着广泛的普遍性。sdRNA的发现拓展了snoRNA的功能,揭示了snoRNA与RNA介导的基因沉默之间的紧密关系,增强了snoRNA在RNA调控网络中的重要性,并为进一步研究RNA调控网络开启了一扇门。 相似文献
6.
RNomics: an experimental approach that identifies 201 candidates for novel, small, non-messenger RNAs in mouse 总被引:34,自引:0,他引:34
Hüttenhofer A Kiefmann M Meier-Ewert S O'Brien J Lehrach H Bachellerie JP Brosius J 《The EMBO journal》2001,20(11):2943-2953
In mouse brain cDNA libraries generated from small RNA molecules we have identified a total of 201 different expressed RNA sequences potentially encoding novel small non-messenger RNA species (snmRNAs). Based on sequence and structural motifs, 113 of these RNAs can be assigned to the C/D box or H/ACA box subclass of small nucleolar RNAs (snoRNAs), known as guide RNAs for rRNA. While 30 RNAs represent mouse homologues of previously identified human C/D or H/ACA snoRNAs, 83 correspond to entirely novel snoRNAS: Among these, for the first time, we identified four C/D box snoRNAs and four H/ACA box snoRNAs predicted to direct modifications within U2, U4 or U6 small nuclear RNAs (snRNAs). Furthermore, 25 snoRNAs from either class lacked antisense elements for rRNAs or snRNAS: Therefore, additional snoRNA targets have to be considered. Surprisingly, six C/D box snoRNAs and one H/ACA box snoRNA were expressed exclusively in brain. Of the 88 RNAs not belonging to either snoRNA subclass, at least 26 are probably derived from truncated heterogeneous nuclear RNAs (hnRNAs) or mRNAS: Short interspersed repetitive elements (SINEs) are located on five RNA sequences and may represent rare examples of transcribed SINES: The remaining RNA species could not as yet be assigned either to any snmRNA class or to a part of a larger hnRNA/mRNA. It is likely that at least some of the latter will represent novel, unclassified snmRNAS: 相似文献
7.
The review considers small nucleolar RNAs (snoRNAs), an abundant group of non-protein-coding RNAs. In association with proteins, snoRNAs determine the two most common nucleotide modifications in rRNA and some other cell RNAs: 2′-O-methylation of ribose and pseudouridylation. In addition, snoRNAs are involved in pre-mRNA cleavage and the telomerase function. Almost all snoRNAs fall into two families, C/D and H/ACA, distinguished by conserved sequence boxes. Although the proteins of C/D and H/ACA snoRNPs have homologous regions, these snoRNPs are assembled differently. The RNA components of RNases P and MRP are also classed with snoRNAs. Another problem considered is the structure and function of small RNAs from Cajal bodies (small organelles associated with the nucleoli), which are similar to snoRNAs. 相似文献
8.
9.
Small nucleolar RNAs (snoRNAs) are an abundant class of non-protein-coding RNAs. In association with proteins they perform two most frequent nucleotide modifications in rRNAs and some other cellular RNAs: 2'-O-ribose methylation and pseudouridylation. SnoRNAs also participate in pre-rRNA cleavage and telomerase functions. Most snoRNAs fall into two families, box C/D and H/ACA, distinguished by the presence of conserved sequence boxes. Although C/D and H/ACA snoRNP proteins contain homologous regions, the assembly of these RNPs significantly differ. In addition, snoRNAs include the RNA component of RNAses P and MRP. The structure and function of small RNPs from Cajal bodies (small organelles associated with nucleoli) similar to snoRNP are also discussed. 相似文献
10.
A snoRNA that guides the two most conserved pseudouridine modifications within rRNA confers a growth advantage in yeast 总被引:6,自引:1,他引:5
Ribosomal RNAs contain a number of modified nucleotides. The most abundant nucleotide modifications found within rRNAs fall into two types: 2'-O-ribose methylations and pseudouridylations. In eukaryotes, small nucleolar guide RNAs, the snoRNAs that are the RNA components of the snoRNPs, specify the position of these modifications. The 2'-O-ribose methylations and pseudouridylations are guided by the box C/D and box H/ACA snoRNAs, respectively. The role of these modifications in rRNA remains poorly understood as no clear phenotype has yet been assigned to the absence of specific 2'-O-ribose methylations or pseudouridylations. Only very recently, a slight translation defect and perturbation of polysome profiles was reported in yeast for the absence of the Psi at position 2919 within the LSU rRNA. Here we report the identification and characterization in yeast of a novel intronic H/ACA snoRNA that we called snR191 and that guides pseudouridylation at positions 2258 and 2260 in the LSU rRNA. Most interestingly, these two modified bases are the most conserved pseudouridines from bacteria to human in rRNA. The corresponding human snoRNA is hU19. We show here that, in yeast, the presence of this snoRNA, and hence, most likely, of the conserved pseudouridines it specifies, is not essential for viability but provides a growth advantage to the cell. 相似文献