Overproduction and translational regulation of rp49 ribosomal protein mRNA in transgenic Drosophila carrying extra copies of the gene.

During Drosophila early development the translation of ribosomal protein mRNAs is regulated specifically and coordinately. In this study we assayed for changes of ribosomal protein rp49 gene expression in flies transformed with extra copies of the gene. RNA blot analysis revealed that the rp49 transcript was overrepresented in most of the transformed fly lines: flies carrying three times more genes than the wild type contained up to seven times more mRNA. The abundance of other ribosomal protein mRNAs was not affected. Despite the large differences in rp49 mRNA content, the proportion of the rp49 mRNA which was associated with polysomes during oogenesis and early embryogenesis did not differ significantly from the wild type, implying that rp49 protein is overproduced in the transgenic flies. The results indicate that the basis for coordinate r-protein gene expression lies in the intrinsic properties of r-protein genes, rather than in a dynamic system that separately modulates the expression of individual genes.