Euglena gracilis chloroplast ribosomal RNA transcription units. I. The location of transfer RNA, 5 S, 16 S, and 23 S ribosomal RNA genes.

The organization of the genes in the rRNA coding region of Euglene gracilis Pringsheim strain Z chloroplast DNA has been determined. 125I labeled 16 S rRNA, 125I labeled 23 S rRNA, and [32P]tRNAs were hybridized to restriction nuclease fragments from cloned chloroplast DNA segments. The coding regions for 16 S and 23 S rRNAs have been located to within 1.75 and 3.1 kbp, respectively. Transfer rRNA genes are located in the 16 S to 23 S rRNA spacer region. Ribosomal RNAs and tRNAs are encoded on the same DNA strand in the 6.2 kbp tandemly repeated rRNA gene region. The order of genes, which is repeated three times in chloroplast DNA, is 16 S rRNA--tRNAS--23 S rRNA--5 S rRNA. Each set of genes is clustered in a region of 5.0 kbp. The organization and size of the genes is as expected if they are all part of a single transcription unit.