Nucleotide sequence of a ‘truncated rRNA operon’ of theEuglena gracilisChloroplast 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 (A1a, I1e) nor parts of the 23S and 5S rRNA genes are found within 557 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-1 endonuclease analysis suggest that the s-16S rDNA region is probably not transcribed into stable s-16S rRNA.

Transfer RNA genes of Euglena gracilis chloroplast DNA

“…Euglena chloroplast DNA contains a truncated rRNA operon 5'-proximal to the tandemly repeated, complete operons (14). This locus lacks the trnI-trnA locus 3'-distal to the 'sl6S' gene, but contains a pseudo trnW-trnI locus in the rDNA leader region (26).…”

Structure and rearrangements of rRNA genes in chloroplast DNA in two strains of Euglena gracilis

“…In the Z strain a 28 bp inverted repeat was found in the leader region of the extra 16S rRNA gene (17). The 3'-end of the gene is followed by a sequence which is homologous with the sequence downstream of the 5S rRNA gene of the complete operons (12,17,6).…”

“…A sequence of 28 bp from the 5'-terminal part of the structural 16S rRNA sequence was found to be inserted into the leader sequence of this gene in an inverted orientation. S l-endonuclease protection analysis suggests that the extra 16S rRNA gene in the Z strain is not transcribed into a stable rRNA (17).…”

A chimeric transcript containing a 16 S rRNA and a potential mRNA in chloroplasts of Euglena gracilis

“…The gene coding for a supplementary 16 S rRNA (s16 S rrn) is 98% homologous with the 16 S rrn genes of the complete rrn operons [28]. All 16 S rrn genes have one BgllI site 181 bp downstream from their 5' -ends (Fig.…”

“…Supplementary 16 S and 5 S rRNA genes (sl6 S and s5 S rrn genes) and in some strains also a partial 23 S rRNA sequence were found upstream of the complete rrn operons [10,12,13]. In the strain Z of Euglenagracilis an inverted repeat of about 100 bp and an open reading frame with the coding capacity for 406 amino acids (ORF406) were found between the 3'-end of the s16 S and the first complete rrn operon [11,28,29]. A sequence of 200 bases upstream of the s16 S rrn gene is homologous with the equivalent region in the complete rrn operons; therefore this supplementary 16 S rrn gene probably has the same promoter as the complete rrn operons.…”