| Summary: | 博士 === 國立陽明大學 === 生命科學系暨基因體科學研究所 === 102 === By Western blotting analysis and the immunofluorescence microscopy observation, we identified that ribosomal protein S20 is a cytoplasmic protein. To view the importance of the cytoplasm nature of S20, we created a nuclear resident S20NLS mutant protein and examined its behavior with respect to small subunit assembly and function. Using an energy depletion and recovery approach to shuttle S20NLS between the nucleus and the cytoplasm, we showed that the joining of S20 to the pre-40S subunit in the cytoplasm was essential for creating a functional small subunit. In addition, we demonstrated that the cytoplasm nature of S20 was required for the late maturation of 18S rRNA using a combining approach of the siRNA knock-down and a co-transfection assay. Furthermore, the Arg62, Arg83, and Arg87 within the putative β-stranded ribbon structure of S20 were involved in the maturation. Our results suggest that the late joining of S20 in the cytoplasm is crucial for 18S rRNA maturation and for making a functionally proficient subunit. It also implies that the order of eukaryotic ribosomal protein assembly may probably execute in a similar order as imposed by the rules of the prokaryotic ribosome map.
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