Poly(adenylic acid)‐Containing RNA of Euglena gracilis during Chloroplast Development

During light‐induced chloroplast development of dark‐grown Euglena gracilis , changes in the polyadenylated RNA distribution have been studied by hybridization of complementary DNA (cDNA) to poly(A)‐containing RNA from different preparations: total cell polyribosomes of dark‐grown cultures illuminated for 0, 1, 6, 24 h, and isolated chloroplasts extracted after 24 h of illumination. The hybridization kinetics revealed three or four frequency classes in the different poly(A)‐containing RNA populations. The high complexity of the poly(A)‐containing RNA sequences synthesized after only 1 h of illumination suggested a transcription mainly from nuclear genome origin. The disribution of poly(A)‐containing RNA was strongly modified after 24 h of illumination and a new class appeared corresponding to abundant sequences. At this stage of the greening, 73% of the poly(A)‐containing RNA sequences were common to the poly(A)‐containing RNA from‐grown cultures; so the sequences synthesized after illumination represented qualitatively a large diversity, but quantitatively, a low proportion of the poly(A)‐containing RNA population. The majority of poly(A)‐containing RNA sequences obtained from isolated chloroplasts was also present in total cell polyadenylated RNA population after 24 h of greening. However. a class corresponding to the most abundant RNA sequences represented 50% of poly(A)‐containing RNA from isolated chloroplasts and only 11% of total cell poly(A)‐containing RNA preparation. The estimated complexities, either for this specific class or for the total polyadenylated RNA population from isolated chloroplasts, suggested the presence of RNA sequences from nuclear origin at the level of chloroplast preparations.