Processing of chloroplast ribosomal RNA transcripts in Euglena gracilis bacillaris.

The ribosomal RNA operons (rrn operons) of Euglena gracilis chloroplasts contain genes for (in order) 16S rRNA, tRNA(Ile), tRNA(Ala),23S rRNA and 5S rRNA. Major sites of cleavage of the primary rrn transcript were identified by Northern blot hybridization and S1-mapping. The presumptive termini of all of the mature products have now been identified. During initial processing in the chloroplast, the primary transcript is cleaved between the two tRNAs and between the 23S and 5S rRNAs so as to separate the sequences found in the different mature rRNAs. Subsequently the tRNAs are separated from the rRNAs, further trimming provides the remaining proper ends, and the 3'-ends of the tRNAs are added.