Abstract
The three tandemly repeated ribosomal RNA operons from the chloroplast genome of Euglena gracilis Klebs, Pringsheim Strain Z each contain a 5 S rRNA gene distal to the 23 S rRNA gene (Gray, P.W., and Hallick, R.B. (1979) Biochemistry 18, 1820-1825). We have cloned two distinct 5 S rRNA genes, and determined the DNA sequence of the genes, their 5'- and 3'-flanking sequences, and the 3'-end of the adjacent 23 S rRNA genes. The two genes exhibit sequence polymorphism at five bases within the "procaryotic loop" coding region, as well as internal restriction endonuclease site heterogeneity. These restriction endonuclease site polymorphisms are evident in chloroplast DNA, and not just the cloned examples of 5 S genes. Chloroplast 5 S rRNA was isolated, end labeled, and sequenced by partial enzymatic degradation. The same polymorphisms found in 5 S rDNA are present in 5 S rRNA. Therefore, both types of 5 S rRNA genes are transcribed and are present in chloroplast ribosomes.
Highlights
The three tandemly repeated ribosomal RNA operons from the chloroplast genome of Euglena gracilis Klebs, Pringsheim Strain 2 each contain a 5 S rRNA gene distal to the 23 S rRNA gene
We were interested in analyzing the nucleotide sequence of the 5 S rRNA genes of Euglena to look for heterogeneity that may exist between genes on the three different repeats.In our analyses, we used restriction mapping
The 5 S rRNA genes of rrnA andB are located on 2.5- separating these 3'-terminalsequences fromthe remainderof kbp EcoRI fragments (EcoL1 and LJ, and on 2.5-kbp the 23 S rRNA gene, and no 4.5 S rRNA species is found in HindIIIfragments(Hind23and 24)
Summary
The twogenesexhibit sequence polymorphism at five bases within the “procaryotic loop” coding region, as well as internal restriction endonuclease site heterogeneity These restrictioenndonuclease site polymorphisms areevident in chloroplast DNA, and not just the cloned examples of 5 S genes. The ribosomal RNA-coding loci of E. gracilis consist of three tandemly repeated units, each containing the genes for the 16 S, 23 S, and 5 S rRNA genes. The repeating unit is 6.2 kbp’ in length and has thecontiguous gene arrangement 16 S rRNA-tRNA”‘-tRNAA’”-23S rRNA-5 S rRNA [13, 14] This gene organization resembles the ribosomal RNA operons of Escherichia coli [15]. We present evidence for the existence of at least two distinct 5 S rRNA genes on the Euglena chloroplast genome. It would appear that both of these genes are transcribed into stable RNAs that are both present in the chloroplasts
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