Changes in the expression of the chloroplast genome of Euglena gracilis during chloroplast development

The transcription program from the chloroplast genome of Euglena gracilis Z during light-induced chloroplast development has been characterized by hybridization of total cell RNA to 3H-labeled chloroplast DNA. Pancreatic DNase activated, purified Euglena chloroplast DNA was enzymatically labeled by Escherichia coli DNA polymerase I with [3H]TTP as a substrate. The [3H]DNA 'hybridization probe" was characterized by the kinetics of its renaturation with purified chloroplast DNA, and the thermal stability of [3H]DNA-DNA, and [3H]DNA-RNA hybrids. The [3H]DNA was hybridized in trace amounts to total cellular RNA extracted from Euglena cells 0, 4, 8, 12, 24, 48, and 72 h after the onset of chloroplast development. A large percentage (17%) of the chloroplast genome was found to be transcribed in dark adapted cells. Development is marked by an initial decrease in the fraction of the genome transcribed followed by an increase to 23% transcribed at the end of 72 h of light growth. Chloroplast RNA transcripts were also characterized by the kinetics of their hybridization to chloroplast DNA. The chloroplast specific RNA population is composed of three abundance classes, and the R0t1/2 for each class varies during the early stages of chloroplast development.