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During the nucleolar maturation of eukaryotic ribosomal RNAs, many selected uridines are converted into pseudouridine by a thus far undefined mechanism. The nucleolus contains a large number of small RNAs (snoRNAs) that share two conserved sequence elements, box H and ACA. In this study, we demonstrate that site-specific pseudouridylation of rRNAs relies on(More)
The nucleolus has long been known as a functionally highly specialized subnuclear compartment where synthesis, posttranscriptional modification, and processing of cytoplasmic rRNAs take place. In this study, we demonstrate that the nucleolus contains all the trans-acting factors that are responsible for the accurate and efficient synthesis of the eight(More)
Telomerase is a ribonucleoprotein reverse transcriptase that uses its RNA component as a template for synthesis of telomeric DNA repeats at the ends of linear eukaryotic chromosomes. Here, fluorescence in situ hybridization demonstrates that in HeLa cancer cells, human telomerase RNA (hTR) accumulates in the nucleoplasmic Cajal bodies (CBs). Localization of(More)
Pseudouridine, the most abundant modified nucleoside in RNA, is synthesized by posttranscriptional isomerization of uridines. In eukaryotic RNAs, site-specific synthesis of pseudouridines is directed primarily by box H/ACA guide RNAs. In this study, we have identified 61 novel putative pseudouridylation guide RNAs by construction and characterization of a(More)
Eukaryotic rRNAs possess numerous post-transcriptionally modified nucleotides. The most abundant modifications, 2'-O-ribose methylation and pseudouridylation, occur in the nucleolus during rRNA processing. The nucleolus contains a large number of small nucleolar RNAs (snoRNAs) most of which can be classified into two distinct families defined by conserved(More)
The two major families of small nucleolar RNAs (snoRNAs), Box C/D and Box H/ACA, are generated in the nucleoplasm and transported to the nucleolus where they function in rRNA processing and modification. We have investigated the sequences involved in the intranuclear transport of Box H/ACA snoRNAs by assaying the localization of injected fluorescent RNAs in(More)
The positive transcription elongation factor b (P-TEFb), a complex of Cdk9 and cyclin T1/T2, stimulates transcription by phosphorylating RNA polymerase II. The 7SK small nuclear RNA, in cooperation with HEXIM1 protein, functions as a general polymerase II transcription regulator by sequestering P-TEFb into a large kinase-inactive 7SK/HEXIM1/P-TEFb complex.(More)
The transcription of eukaryotic protein-coding genes involves complex regulation of RNA polymerase (Pol) II activity in response to physiological conditions and developmental cues. One element of this regulation involves phosphorylation of the carboxy-terminal domain (CTD) of the largest polymerase subunit by a transcription elongation factor, P-TEFb, which(More)