Euglena gracilis chloroplast transfer RNA transcription units. Nucleotide sequence analysis of a tRNATyr-tRNAHis-tRNAMet-tRNATrp-tRNAGlu-tRNAGly gene cluster

Abstract

A tRNA coding locus in the Bam-Sal 9 region of Euglena gracilis Pringsheim strain Z chloroplast DNA was chosen for detailed study. This DNA contains the previously mapped tRNA coding sequences of the adjacent Euglena chloroplast EcoRI products of EcoV and EcoH (Orozco, E. M., Jr., and Hallick, R. B. (1982) J. Biol. Chem. 257, 3258-3264). The 3.2-kilobase pair Bam-Sal 9 fragment was cloned into the BamHI and SalI cut plasmid vector pBR322, resulting in the recombined plasmid pPG76. The tRNA coding locus was mapped to a region of Bam-Sal 9 that contains portions of both EcoH and EcoV. The DNA sequence of 1-kilobase pair Bam-Sal 9, containing the entire tRNA coding locus, was determined. A cluster of six tRNA genes was found. The gene organization is as follows, where bp is base pair: tRNATyrGUA-64 bp spacer-tRNAHisGUG-14 bp spacer-tRNAMetCAU-4 bp spacer-tRNATrpCCA-27 bp spacer-tRNAGluUUC-6 bp spacer-tRNAGlyUCC. The tRNAMetCAU is believed to be an elongator tRNA. The first four genes are within EcoV. The EcoRI cleavage site that separates EcoV and EcoH is in the tRNAGlu gene. The tRNAGly gene is in EcoH. This is the largest known chloroplast tRNA gene cluster.