Partially processed pre-rRNA is preserved in association with processing components in nucleolus-derived foci during mitosis.
Previous studies showed that components implicated in pre-rRNA processing, including U3 small nucleolar (sno)RNA, fibrillarin, nucleolin, and proteins B23 and p52, accumulate in perichromosomal regions and in numerous mitotic cytoplasmic particles, termed nucleolus-derived foci (NDF) between early anaphase and late telophase. The latter structures were analyzed for the presence of pre-rRNA by fluorescence in situ hybridization using probes for segments of pre-rRNA with known half-lives. The NDF did not contain the short-lived 5'-external transcribed spacer (ETS) leader segment upstream from the primary processing site in 47S pre-rRNA. However, the NDF contained sequences from the 5'-ETS core, 18S, internal transcribed spacer 1 (ITS1), and 28S segments and also had detectable, but significantly reduced, levels of the 3'-ETS sequence. Northern analyses showed that in mitotic cells, the latter sequences were present predominantly in 45S-46S pre-rRNAs, indicating that high-molecular weight processing intermediates are preserved during mitosis. Two additional essential processing components were also found in the NDF: U8 snoRNA and hPop1 (a protein component of RNase MRP and RNase P). Thus, the NDF appear to be large complexes containing partially processed pre-rRNA associated with processing components in which processing has been significantly suppressed. The NDF may facilitate coordinated assembly of postmitotic nucleoli.
Dundr
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Department of Biochemistry, University of Mississippi Medical Center, Jackson, Mississippi 39216-4505, USA.
Olson
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D020121:5' Untranslated Regions; D000818:Animals; D051017:Apoptosis Regulatory Proteins; D002352:Carrier Proteins; D002460:Cell Line; D002466:Cell Nucleolus / Q000378:metabolism; D004722:Endoribonucleases / Q000378:metabolism; D000882:Haplorhini; D006801:Humans; D008938:Mitosis / Q000502:physiology*; D012322:RNA Precursors; D012323:RNA Processing, Post-Transcriptional; D016337:RNA, Catalytic / Q000378:metabolism; D012337:RNA, Ribosomal, 18S; D012339:RNA, Ribosomal, 28S; D012342:RNA, Small Nuclear; D043262:Ribonuclease P; D012261:Ribonucleoproteins / Q000032:analysis
D020121:5' Untranslated Regions; D051017:Apoptosis Regulatory Proteins; D002352:Carrier Proteins; C490350:POP1 protein, human; D012322:RNA Precursors; D016337:RNA, Catalytic; D012337:RNA, Ribosomal, 18S; D012339:RNA, Ribosomal, 28S; D012342:RNA, Small Nuclear; D012261:Ribonucleoproteins; D004722:Endoribonucleases; C058330:mitochondrial RNA-processing endoribonuclease; C468368:RPP14 protein, human; D043262:Ribonuclease P