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© The Rockefeller University Press,
0021-9525/2001//169 $5.00
The Journal of Cell Biology, Volume 153, Number 1,
, 2001 169-176
Original Article |
Nucleolar Components Involved in Ribosome Biogenesis Cycle between the Nucleolus and Nucleoplasm in Interphase Cells
s-huang2{at}northwestern.edu
We examined the mobilities of nucleolar components that act at various steps of the ribosome biogenesis pathway. Fluorescence recovery after photobleaching (FRAP) and fluorescence loss in photobleaching (FLIP) analyses demonstrate that factors involved in rRNA transcription (upstream-binding factor [UBF]), processing (nucleolin, fibrillarin, and RNase MRP subunits, Rpp29), and ribosome assembly (B23) exchange rapidly between the nucleoplasm and nucleolus. In contrast, the mobilities of ribosomal subunit proteins (S5, L9) are much slower. Selective inhibition of RNA polymerase I transcription does not prevent the exchanges but influences the rates of exchange differentially for different nucleolar components. These findings suggest that the rapid exchange of nucleolar components between the nucleolus and nucleoplasm may represent a new level of regulation for rRNA synthesis. The different dynamic properties of proteins involved in different steps of ribosome biogenesis imply that the nucleolar association of these proteins is due to their specific functional roles rather than simply their specific nucleolar-targeting events.
Key Words: nucleolar proteins ribosome biogenesis dynamics living cells
© 2001 The Rockefeller University Press
Abbreviations used in this paper: ActD, actinomycin D; FLIP, fluorescence loss in photobleaching; GFP, green fluorescent protein; NOR, nucleolar-organizing region; pol, RNA polymerase; RFI, relative fluorescence intensity; TBP, TATA-binding protein; UBF, upstream-binding factor.
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