Involvement of N-terminal region in mitochondrial targeting of rice RPS10 and RPS14 proteins

Abstract

We have investigated targeting signal of rice mitochondrial ribosomal proteins, RPS10 and RPS14. Their predicted protein structures show that RPS14 has a cleavable N-terminal extension whereas RPS10 does not, and that the both proteins contain several α-helix structures. To know which regions are involved in protein targeting into mitochondria, subcellular localization of the two proteins was examined in vivo by using a green fluorescent protein (GFP). A portion of RPS10 or RPS14 was fused to the GFP and introduced into tobacco BY-2 cells. Localization of fusion proteins was visualized by GFP fluorescence. When the N-terminal part of RPS10 (amino acid position 1–56) was fused to GFP, resultant GFP fusion proteins were detected specifically in mitochondria. In contrast, no such localization was found when the C-terminal part of RPS10 was fused to GFP. GFP fusion proteins were clearly localized to mitochondria when the N-terminal region of RPS14 (amino acid position 1–48) was fused to GFP. Introduction of sequence alterations into their N-terminal regions abolished the specificity of mitochondrial targeting. These results strongly suggest that the N-terminal region plays an important role for the targeting of the ribosomal proteins into plant mitochondria irrespective of the N-terminal extension.