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The 26S proteasome, a protein complex consisting of a 20S proteasome and a pair of 19S regulatory particles (RP), is involved in ATP-dependent proteolysis in eukaryotes. In yeast, theRP contains six different ATPase subunits and, at least, 11 non-ATPase subunits. In this study, we identi®ed the rice homologs of yeast RP subunit genes from the rice expressed sequence tag (EST) library. | Eur. J. Biochem. 269 1474-1483 2002 FEBS 2002 Identification of the 19S regulatory particle subunits from the rice 26S proteasome Tadashi Shibahara Hiroshi Kawasaki and Hisashi Hirano Yokohama City University Kihara Institute for Biological Research Graduate School of Integrated Science Japan The 26S proteasome a protein complex consisting of a 20S proteasome and a pair of 19S regulatory particles RP is involved in ATP-dependent proteolysis in eukaryotes. In yeast the RP contains six different ATPase subunits and at least 11 non-ATPase subunits. In this study we identified the rice homologs of yeast RP subunit genes from the rice expressed sequence tag EST library. The complete nucleotide sequences of the homologs for five ATPase subunits OsRpt1 OsRpt2 OsRpt4 OsRpt5 and OsRpt6 and five non-ATPase subunits OsRpn7 OsRpn8 OsRpn10 OsRpn11 and OsRpn12 and the partial sequences of one ATPase subunit OsRpt3 and six non-ATPase subunits OsRpn1 OsRpn2 OsRpn3 OsRpn5 OsRpn6 and OsRpn9 were determined. Gene homologs of four ATPase subunits OsRpt1 OsRpt2 OsRpt4 and OsRpt5 and three non-ATPase subunits OsRpn1 OsRpn2 and OsRpn9 were found to be encoded by duplicated genes. The rice RP was purified by immunoaffinity chromatography with a Protein A column immobilized antibody against rice 20S protea-some and the subunit composition was determined. The homologs obtained from the rice EST library were identified as genes encoding subunits of RP purified from rice including the both products of duplicated genes by using electrospray ionization quadrupole time-of-flight mass spectrometry. Post-translational modifications and processing in rice RP subunits were also identified. Various types of RP complex with different subunit compositions are present in rice cells suggesting the multiple functions of rice proteasome. Keywords proteasomes rice gene duplication purification immunoaffinity chromatography. All organisms possess highly selective proteolytic systems which are essential for .
