Nucleotide sequence of four ribosomal protein L27 cDNAs from growing axillary buds of pea.

Abstract

The small and large subunits of the eukaryotic ribosome contain a total of three to four rRNA molecules and 70 to 80 ribosomal proteins, which are required in stoichiometric amounts (Mager, 1988). Expression of ribosomal protein genes in plants has been correlated with active growth and cell division in a variety of tissues and organs, including auxin-treated soybean hypocotyls (Gantt and Key, 19851, developing maize embryos (Larkin et al., 1989), cytokinintreated soybean cell cultures (Crowell et al., 19901, and tomato shoot apical meristems (Flemming et al., 1993). Ribosomal protein genes in plants and other organisms generally are expressed coordinately (Gantt and Key, 1985; Mager, 1988). Some ribosomal proteins are encoded by single-copy genes (Hwang and Goodman, 1993), whereas otliers are encoded by small gene families. For example, the Brussica rpSl5a (for ribosomal protein S15a) gene family contains two expressed members that encode identical polypeptides (Bonham-Smith et al., 1992). Based on Southern blot analysis, the maize rpS14 gene family may contain as many as six members, three of which have been shown to be expressed; the two rpS14 cDNA clones that have been sequenced encode peptides that differ in size and sequence (Larkin et al., 1989). We show here that the pea (Pisum sativum) rpL27 family contains at least five expressed members, the largest ribosomal protein gene family from any plant for which sequence data are available. We previously isolated an rpL27 cDNA from growing axillary buds of pea (rpL27-1; Stafstrom and Sussex, 1992). When compared to a rat gene, rpL27-1 lacked a single nucleotide at the 5’ end of the coding sequence (TG instead of ATG). To identify the complete coding sequence corresponding to this gene, two different cDNA libraries were screened using rpL27-1 as a probe. Four additional clones were isolated; DNA sequences of these clones were distinct from each other and from rpL27-1 (Table I). Three of these clones (rpL27-3, rpL274, and rpL27-5) contain an ATG at the expected position. In addition, rpL27-3 and rpL27-5 contain an in-frame stop codon at position -12. Nucleotide sequence identity among the five rpL27 clones is greater than 96%. The deduced amino acid sequences of the four (nearly) full-length clones differ from each other at one to three residues (rpL27-2, which encodes only the C-terminal49 amino acids,