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Cajal (coiled) bodies are conserved subnuclear organelles that are present in the nucleoplasm of both animal and plant cells. Although Cajal bodies were first described nearly 100 years ago, their function has remained largely speculative. Here, we describe a novel class of human small nuclear RNAs that localize specifically to Cajal bodies. The small Cajal(More)
This report examines the distribution of an RNA polymerase I transcription factor (upstream binding factor; UBF), pre-rRNA processing factors (nucleolin and fibrillarin), and pre-rRNAs throughout mitosis and postmitotic nucleologenesis in HeLa cells. The results demonstrate that nucleolin, fibrillarin, and pre-rRNAs synthesized at G2/M phase of the previous(More)
Transcription and splicing of messenger RNAs are temporally and spatially coordinated through the recruitment by RNA polymerase II of processing factors. We questioned whether RNA polymerase I plays a role in the recruitment of the ribosomal RNA (rRNA) processing machinery. During Xenopus laevis embryogenesis, recruitment of the rRNA processing machinery to(More)
RNA polymerases are key multisubunit cellular enzymes. Microscopy studies indicated that RNA polymerase I assembles near its promoter. However, the mechanism by which RNA polymerase II is assembled from its 12 subunits remains unclear. We show here that RNA polymerase II subunits Rpb1 and Rpb3 accumulate in the cytoplasm when assembly is prevented and that(More)
Site-specific post-transcriptional conversion of uridines to pseudouridine in ribosomal RNAs and small nuclear RNAs (snRNAs) is directed by guide RNAs which possess the conserved box H and ACA sequence elements and fold into the consensus 'hairpin-hinge-hairpin-tail' secondary structure. Here, we describe an unusual mammalian pseudouridylation guide RNA,(More)
Post-transcriptional synthesis of 2'-O-methylated nucleotides and pseudouridines in Sm spliceosomal small nuclear RNAs takes place in the nucleoplasmic Cajal bodies and it is directed by guide RNAs (scaRNAs) that are structurally and functionally indistinguishable from small nucleolar RNAs (snoRNAs) directing rRNA modification in the nucleolus. The scaRNAs(More)
To better understand intranuclear-targeting mechanisms, we have studied the transport of U3 snoRNA in human cells. Surprisingly, we found that PHAX, the snRNA export adaptor, is highly enriched in complexes containing m7G-capped U3 precursors. In contrast, the export receptor CRM1 is predominantly bound to TMG-capped U3 species. In agreement, PHAX does not(More)
During the early development of Xenopus laevis, we followed in individual nuclei the formation of a nucleolus by examining simultaneously its structural organization and its transcriptional competence. Three distinct situations were encountered with different frequencies during development. During the first period of general transcriptional quiescence, the(More)
RNA-binding proteins of the L7Ae family are at the heart of many essential ribonucleoproteins (RNPs), including box C/D and H/ACA small nucleolar RNPs, U4 small nuclear RNP, telomerase, and messenger RNPs coding for selenoproteins. In this study, we show that Nufip and its yeast homologue Rsa1 are key components of the machinery that assembles these RNPs.(More)