A transfer RNAArg gene of Pelargonium chloroplasts, but not a 5S RNA gene, is efficiently transcribed after injection into Xenopus oocyte nuclei.

We present the primary structure of a chloroplast tRNAArgACG gene of the plant, Pelargonium zonale, and its faithful expression in Xenopus oocyte nuclei. This tRNAArg gene is located 250 bp downstream of a 5S RNA gene within a cloned 5kb long ribosomal DNA segment (Fig. 1). The Pelargonium tRNAArg gene shares 97% and 86% sequence homology with tRNAArgACG genes of Spirodela oligorhiza and Euglena gracilis chloroplasts, respectively, and also extensive homology (70%) with the corresponding gene of E. coli. It lacks an intervening sequence and, like eukaryotic tRNA genes, does not code for the 3' terminal CCA nucleotides. Moreover, the chloroplast tRNAArg gene carries all the sequence elements essential for transcription by vertebrate RNA polymerase III since it is efficiently expressed in Xenopus oocyte nuclei, even in the presence of 1 microgram/ml alpha-amanitin. In Xenopus oocyte nuclei, no transcripts of the chloroplast 5S RNA gene were detected.