Internal structural organization of chloroplast DNA from Euglena gracilis Z

The arrangement of base-sequences in the chloroplast deoxyribonucleic acid from Euglena gracilis Z was investigated by analyzing the bimodal profile of chloroplast deoxyribonucleic acid in an alkaline CsCl density gradient. The three main fractions in the alkaline gradient contain both single-stranded self-complementary base-sequences and base-sequences that are not self-complementary. Four single-stranded self-complementary deoxyribonucleic acid components were isolated from alkaline CsCl preparative density gradients. A fifth component was derived by annealing two fractions containing deoxyribonucleic acid that was not self-complementary. The five fractions corresponded to the five components of total chloroplast deoxyribonucleic acid that exhibited differential thermal denaturation. The results indicate that these five components are not interspersed throughout the genome in small segments but that they exist as relatively large segments. This implies that the chloroplast deoxyribonucleic acid contains tandemly arranged segments differing in base-composition.