Nucleotide sequence of a cDNA for a P2 60S acidic ribosomal protein from Parthenium argentatum.

In screening a stem-bark cDNA library from guayule (Parthenium argentatum) for genes involved in isoprenoid biogenesis, we isolated a full-length gene for a P2 60s acidic ribosomal protein that shows sequence similarity to vertebrate (Rich and Steitz, 1987), invertebrate (Qian et al., 1987), and yeast (Beltrame and Bianchi, 1987, 1990; Remacha et al., 1988) 605 acidic ribosomal proteins (Table I). The guayule P2 sequence is a full-length cDNA; a partia1 cDNA has been described for Arabidopsis (C. Bardet, M. Axelos, D. Tremousaygue, M. Lebas, T. Lagravere, and B. Lescure, unpublished data; EMBL accession number 217464) with 65.5% identity at the nucleic acid level and 54.5% identity and 74.5% similarity at the amino acid level. Our interest in this gene extends to its potential use in experimental studies of Parthenium, from which few genes are at present available. Being a ribosomal protein, it should display minimal variations in expression and thus serve as a suitable intemal control for gene expression studies in this species. The P2 60s acidic ribosomal protein plays a crucial role in the elongation step of protein synthesis. The P2 proteins exist as heterodimers composed of a and ,tl subunits. Comparison of the P2 Parthenium sequence with both the a (Beltrame and Bianchi, 1987) and ,tl (Beltrame and Bianchi, 1990) subunits of fission yeast shows nearly the same identity, 52.7 versus 50.9%, respectively, making it difficult to classify the guayule protein as P2 a or P2 0. Comparison of the P2 Parthenium sequence to the human LA2 protein (Rich and Steitz, 1987) shows 59.0% identity at the nucleic acid level and 54.5% identity and 79.5% similarity on the amino acid level, with a similar level of identity for the Drosophila gene (Qian et al., 1987).