Location of Ribosomal Protein S6 in Higher Eukaryocyte Nucleolus not Related to Its Phosphorylation

Zhang Duo^1,2, Gao Lihua¹, Shao Yong¹, Xi Yongyi¹, Xu Zhaoping¹, Chen Huipeng¹, Hu Xianwen^1*

¹Beijing Institute of Biotechnology, Beijing 100071, China; ²Clinical Genetic Research Center, Fuzhou General Hospital of Nanjing Military Region, Fuzhou 350025, China

Abstract: Ribosomal protein S6 (rpS6) was considered as a component of the cytosolic 40S ribosomal subunit. However， using the technique of proximity ligation in situ assay and immunofluorescence analysis， the studies presented here revealed that rpS6 was not only a component of the 40S ribosomal subunit， but also colocalized and interacted with Mpp10， an essential component of U3 snoRNP. The rpS6 protein had five phosphorylation sites at the C terminus. In order to identify the relationship of distribution in nucleolus with its phosphorylation， we constructed two mutations of rpS6. One was rpS6A whose five phosphorylatable serine residues sites were replaced by alanine residues， the other was rpS6D whose five phosphorylatable serine residues sites were replaced by aspartic acides. The rpS6， rpS6A and rpS6D protein were expressed as fusion with EGFP and HA tag， respectively. The results showed that not only rpS6 fusion protein but also rpS6A and rpS6D fusion protein could distribute in nucleolus， suggesting the phosphorylation could not affect rpS6 protein entering into nucleolus. This work made a way for the study of rpS6 function in nucleolus in future.

CSTR: 32200.14.cjcb.2012.02.0002