Abstract
RNA transcription in Euglena gracilis chloroplasts has been characterized by hybridization of RNA from cells at different stages of chloroplast development to (3)H-labeled chloroplast DNA restriction endonuclease fragments. Chloroplast DNA was digested into five 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 [(3)H]dTTP as a substrate. RNA was isolated from dark-adapted Euglena cells, and from cells at an early (4 hr) and a late (72 hr) stage of light-induced chloroplast development. The RNAs were hybridized in solution to each (3)H-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 RNAs (i) continuously present throughout development, (ii) induced at the onset of development, (iii) repressed early in development, and (iv) induced late in development.