Isolation and molecular characterisation of the gene encoding the cytoplasmic ribosomal protein S28 in Prunus persica [L.]Batsch

RT-PCR was performed on Peach (Prunus persica [L.] Batsch) RNA to isolate c DNAs corresponding to transcripts which are differentially expressed in lea ves borne on basal and apical shoots. A gene was identified which was more highly expressed in the leaves of basal shoots, and codes for the cytoplasm ic protein S28 present in the small ribosomal subunit. The 5' leader region s of RPS28 mRNAs were found to harbour 8-11 pyrimidine tracts, which sugges ted similarities to regulatory stretches that control the translation of mR NAs for ribosomal proteins in animals. The peach S28 is encoded by two intr on-containing genes, which are both transcribed in mitotically active tissu es such as developing leaves and roots. In situ hybridisation to shoot vege tative apices and the measurement of nucleus/nucleolus ratios indicated tha t RPS28 expression was confined to areas undergoing active cell division. T he mature RPS28 mRNA was detected as a single species in actively dividing tissues such as apical tips, developing leaves, vegetative buds, stamens, d eveloping fruits and roots. In contrast, accumulation of a precursor RNA, i n the presence of the mature product, was found in fully expanded leaves an d subtending stems, while only the precursor species was detected in severa l late-stage tissues. This phenomenon suggested that expression of the matu re RNA is controlled at the level of splicing and turnover of the precursor RNA. This is similar to the mode of regulation of ribosomal protein genes in animals.