Transcription program of the chloroplast genome of Euglena gracilis during chloroplast development

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Abstract
RNA transcription in E. gracilis chloroplasts was characterized by hybridization of RNA from cells at different stages of chloroplast development to 3H-labeled chloroplast DNA restriction endonuclease fragments. Chloroplast DNA was digested into 5 fragments of 53,000, 35,000, 25,000, 10,000 and 6900 base pairs with Pst I. The 53,000 base-pair DNA was further cleaved by BamHI digestion. Eight different DNA fragments, of known restriction nuclease map location and accounting for the entire genome, were labeled in vitro by means of the nick translation reaction of DNA polymerase I with [3H]dTTP as a substrate. RNA was isolated from dark-adapted Euglena cells, and from cells at an early (4 h) and a late (72 h) stage of light-induced chloroplast development. The RNA were hybridized in solution to each 3H-labeled chloroplast DNA fragment. From the extents and kinetics of the reactions, a temporal program for RNA transcription from defined regions of the chloroplast genome could be described. Different classes of transcription units are present, including RNA continuously present throughout development, induced at the onset of development, repressed early in development and induced late in development.