The chloroplast glutamate tRNA gene required for δ-aminolevulinate synthesis

Abstract

The first major intermediate in the tetrapyrrole biosynthetic pathway is δ-aminolevulinate (δ-ALA). The synthesis of δ-ALA in greening barley requires an RNA (δ-ALA-RNA) which is aminoacylated with glutamate by a tRNA ligase. δ-ALA-RNA isolated from barley plastids and a synthetic nucleotide oligomer were used as hybridization probes to isolate the gene encoding δ-ALA-RNA from a collection of barley DNA chloroplast clones. Sequence of the barley δ-ALA-RNA reveals a typical tRNA sequence which is identical to the wheat glutamate tRNA gene. The tyrosine and aspartate tRNA genes are closely linked to δ-ALA-RNA on a 1.6 kb HindIII-EcoRI restriction fragment. The glutamate tRNA gene is transcribed in the dark and in the light under all the conditions tested. S1 mapping was used to locate the potential regulatory sequences and to establish that the three tRNAs are processed from a single precursor RNA. A single gene encodes the δ-ALA-RNA which functions in δ-ALA synthesis and the glutamate tRNA which functions in chloroplast protein synthesis. The two RNA products may differ in posttranscriptional modifications.