Nucleotide sequence of a ‘truncated rRNA operon’ of the<i>Euglena gracilis</i>Chloroplast genome

Abstract

An extra 16S rRNA gene (s-16S rDNA) from the Euglena gracilis chloroplast genome and several hundred positions of its flanking regions have been sequenced. The structural part has 1486 positions and is to 98% homologous in its sequence with the 16S rRNA gene in functional chloroplast rRNA operons. Sequences of about 200 positions upstream and 15 positions downstream of the structural part of the s-16S rRNA gene region are highly homologous with corresponding parts in the functional operon. Neither tRNA genes (Ala, lie) nor parts of the 2 3S and 5S rRNA genes are found within 5S7 positions after the 3' end of the S-16S rRNA gene, i.e., the 330 bp homology, observed in electron microscopic studies of heteroduplexes (4), between the S-16S rDNA downstream region and the 6.2 kb repeated segment containing the functional rRNA operon, must be due to a DNA stretch in the interoperon spacer. A structural model of the "truncated rRNA operon" is presented. Results from S-l endonuclease analysis suggest that the S-16S rDNA region is probably not transcribed into stable S-16S rRNA.