Nucleotide sequence of a rice acidic ribosomal phosphoprotein P0 cDNA.

The eukaryotic 38-kD acidic ribosomal protein PO is localized to the stalk of the 60s ribosomal subunit, forming a pentameric complex with dimers of 13-kD acidic ribosomal proteins P1 and P2 (Rich and Steitz, 1987). P1 (P2) and PO are analogous to Escherichia coli ribosomal protein L7/L12, and L10, respectively, and are thought to have the same functions as their prokaryotic counterparts, i.e. binding to 28s rRNA, interaction with translation factors, promotion of aminoacyl-tRNA binding, and association with GTP-binding activity (Sanchez-Madrid et al., 1979; MacConnell and Kaplan, 1982). The PO gene has been cloned from many species such as human (Rich and Steitz, 1987), yeast (Mitsui et al., 1989), rat (Wool et al., 1991), Drosophila (Grabowski et al., 1991), Typanosoma (Schijman and Levin, 1992), and the dicotyledonous plant Chenopodium rubrum (Kaldenhoff and Richter, 1990). However, no reports have been presented of PO gene isolated from a monocotyledonous plant. We have camed out the random sequencing of cDNA clones derived from the anther-specific cDNA library of the graminaceous monocot rice (Oryza sativa L.) (Tsuchiya et al., 1992). By comparing partia1 sequences of cDNA clones to the GenBank data base, we found one clone (YK704) that is similar to the PO protein gene. Thus, we were prompted to determine the complete nucleotide sequence of YK704 (Table I). The cDNA is 1220 bp in length, and the deduced open reading frame encodes a 34-kD protein of 319 amino acid residues. The nucleotide sequence shows 70% identity with that of Chenopodium, 60% with Drosophila and human, and 54% with yeast. The GC contents in the coding region and the third position of the codon are 55 and 70%, respectively. In the case of the dicotyledonous plant Chenopodium, the GC content in the coding region is 4875, and the third position of the codon shows 49% GC. Thus, the rice PO gene has an apparent GC bias at the third position of the codon. As reported for other acidic ribosomal PO proteins (Rich and Steitz, 1987; Mitsui et al., 1989; Wool et al., 1991), rice PO protein appears to be hydrophobic because of the high content of hydrophobic amino acid residues such as Ala (9.7%), Val(10.3%), and Leu (9.7%). The deduced amino acid sequence of rice PO shows 68%