We constructed an overexpression system for human ribosomal phosphoprotein P0, together with P1 and P2, which is crucially important for translation. Genes for these proteins, fused with the glutathione S-transferase (GST)-tag at the N-terminus, were inserted into baculovirus and introduced to insect cells. The fusion proteins, but not the proteins without the tag, were efficiently expressed into cells as soluble forms. The fusion protein GST-P0 as well as GST-PI/GST-P2 was phosphorylated in cells as detected by incorporation of P-32 and reactivity with monoclonal anti-phosphoserine antibody. GST-P0 expressed in insect cells, but not the protein obtained in Escherichia coli, had the ability to form a complex with PI and P2 proteins and to bind to 28S rRNA. Moreover, the GST.P0-P1-P2 complex participated in high eEF-2-dependent GTPase activity. Baculovirus expression systems appear to provide recombinant human PO samples that can be used for studies on the structure and function. (C) 2004 Elsevier Inc. All rights reserved.