Expression and processing of the chloroplast ribosomal RNAs of Euglena gracilis.

Among the genes that have been the most intensively studied are undoubtedly those of the rrn operons, which encode the ribosomal RNAs (rRNAs). The chloroplast rRNA genes of Euglena gracilis have been well characterized at the DNA level and show marked structural similarities to prokaryotic rrn genes from which they are thought to have originated. By studying the transcription and processing of the chloroplast rrn genes of Euglena, one can learn more about chloroplast rrn gene regulation and how it compares with the better characterized prokaryotic systems. Chloroplast RNA was isolated from cells grown under a variety of conditions and the 5$\sp\prime$- and 3$\sp\prime$-ends of primary, intermediate and mature rrn transcription products were determined by northern blot hybridization, S1-mapping, and in vitro capping. The site of transcription initiation and the sites of RNA processing were the same under all growth conditions examined. Transcription of the rrn operons initiates at a single site 54 nucleotides upstream of the mature 5$\sp\prime$-end of the 16S rRNA. The start site is part of a sequence that has been shown previously to have evolved from sequences in a Euglena tRNA operon elsewhere on the chloroplast chromosome. This rrn leader sequence including the start of transcription and putative promoter sequences is exactly duplicated (102 of 103 base pairs) near the chloroplast DNA's origin of replication. The similar sequences suggest that transcription may initiate at this site near the replication origin and its location there suggests that such transcription may be involved in DNA replication. Northern blots of chloroplast RNA show two abundant RNAs of 1,500 and 1,700 nucleotides homologous to the 16S rRNA. Hybridization with a synthetic oligonucleotide and S1 analysis of the 16S to 23S spacer show that the larger RNA results from incomplete 3$\sp\prime$-processing of the 16S rRNA.PhDBiological SciencesBiologyMolecular biologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/128164/2/8812944.pd