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.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46969/1/294_2004_Article_BF00419917.pd

Initiation of rrn transcription in chloroplasts of Euglena gracilis bacillaris

The site of initiation of chloroplast rRNA synthesis was determined by Sl-mapping and by sequencing primary rRNA transcripts specifically labeled at their 5′-end. Transcription initiates at a single site 53 nucleotides upstream of the 5'-end of the mature 16S rRNA under all growth conditions examined. The initiation site is within a DNA sequence that is highly homologous to and probably derived from a tRNA gene-region located elsewhere in the chloroplast genome. A nearly identical sequence (102 of 103 nucleotides) is present near the replication origin. The near identity of the two sequences suggests a common mode for control of transcription of the rRNA genes and initiation of chloroplast DNA replication. The related sequence in the tRNA gene-region does not appear to serve as a transcript initiation site.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46967/1/294_2004_Article_BF00521275.pd