Comparative Studies on tRNAs and Aminoacyl-tRNA Synthetases from Various Photosynthetic Organisms

Abstract

Chloroplasts have their own protein synthesizing system, using chloroplast-specific tRNAs which are different from their cytoplasmic counterparts and are coded for by chloroplast DNA (Weil, 1979; Weil and Parthier, 1982). Total chloroplast tRNA can be fractionated by two-dimensional polyacrylamide gel electrophoresis (Burkard et al., 1982) into individual tRNAs, which can be recovered from the gel, identified by aminoacylation and labeled with 32P at their 3′ end using α-32P-ATP and tRNA nucleotidyl transferase (Mubumbila et al., 1980). Each labeled tRNA can then be hybridized to DNA fragments which have been generated by the action of a restriction endonuclease on chloroplast DNA, fractionated by agarose gel electrophoresis, and transferred to nitrocellulose strips. As the position of these fragments on the circular map of the chloroplast chromosome has been previously determined, this approach allows the localization of the tRNA genes. Such a tRNA gene map was first established in the case of the spinach chloroplast genome (Driesel et al., 1979), which is a circular molecule containing two inverted repeats; each of these inverted repeats contains a set of ribosomal RNA genes, and the spacer located between the 16S and the 23S rRNA gene was shown to contain a tRNAIle gene (Bohnert et al., 1979). Such tRNA gene mapping studies have now been extended to the chloroplast genomes of other photosynthetic organisms.