A mitochondrial-targeting signal is present in the non-catalytic domain of the MELK protein kinase.
MELK is a cell cycle-regulated protein kinase involved in cell cycle progression, proliferation, tumor growth and mRNA splicing. MELK is localized in the cytoplasm and the nucleus during interphase and at the cell cortex during anaphase and telophase. In this report, we show that the regulatory domain of Xenopus MELK when tagged at its C-terminus with the green fluorescent protein (GFP), co-localizes with mitochondria in Xenopus XL2 cells. Significantly, the presence of a mitochondrial targeting signal at the N-terminus of this fusion protein was predicted by bioinformatics analyses. In agreement with previous reports on mitochondrial proteins, placing the GFP at the N-terminus inhibited the mitochondrial targeting of the MELK fragment and, furthermore, the regulatory domain without a tag co-localizes with mitochondria. These results demonstrate the presence of a mitochondrial targeting signal at the N-terminus of the MC domain of MELK. This mitochondrial targeting signal was also functional in human HeLa cells.
Chartrain
Isabelle
I
CNRS UMR 6061 Génétique et Développement, Université de Rennes 1, IFR140 GFAS, Faculté de Médecine, 2 avenue du Professeur Léon Bernard, CS 34317, 35043 Rennes Cedex, France.
Blot
Joëlle
J
Lerivray
Hubert
H
Guyot
Nicolas
N
Tassan
Jean-Pierre
JP
D000818:Animals; D020134:Catalytic Domain; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D008928:Mitochondria / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry / Q000378:metabolism*; D021382:Protein Sorting Signals; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D014981:Xenopus / Q000378:metabolism*; D029867:Xenopus Proteins / Q000737:chemistry / Q000378:metabolism*
D021382:Protein Sorting Signals; D029867:Xenopus Proteins; D049452:Green Fluorescent Proteins; D017346:Protein Serine-Threonine Kinases