Late-assembly of human ribosomal protein S20 in the cytoplasm is essential for the functioning of the small subunit ribosome.
Using immuno-fluorescent probing and Western blotting analysis, we reveal the exclusive cytoplasm nature of the small subunit ribosomal protein S20. To illustrate the importance of the cellular compartmentation of S20 to the function of small subunit 40S, we created a nuclear resident S20NLS mutant gene and examined polysome profile of cells that had been transfected with the S20NLS gene. As a result, we observed the formation of recombinant 40S carried S20NLS but this recombinant 40S was never found in the polysome, suggesting such a recombinant 40S was translation incompetent. Moreover, by the tactic of the energy depletion and restoration, we were able to restrain the nuclear-resided S20NLS in the cytoplasm. Yet, along a progressive energy restoration, we observed the presence of recombinant 40S subunits carrying the S20NLS in the polysome. This proves that S20 needs to be cytoplasmic in order to make a functional 40S subunit. Furthermore, it also implies that the assembly order of ribosomal protein in eukaryote is orderly regulated.
Institute of Genome Sciences, School of Life Sciences, National Yang-Ming University, Taipei, Taiwan, ROC.
Lin-Ru
LR
Tai
Chang-Wei
CW
Chou
Jing-Ying
JY
Wu
Ralph
R
Kirby
Alan
A
Lin
D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D003593:Cytoplasm / Q000378:metabolism*; D006801:Humans; D012269:Ribosomal Proteins / Q000378:metabolism*; D054682:Ribosome Subunits, Small, Eukaryotic / Q000378:metabolism*
D012269:Ribosomal Proteins; C029611:ribosomal protein S20
ATP-depletion; Cytoplasmic ribosomal protein S20; Energy depletion/restoration; Polysome assay; Ribosome assembly