Poly (Adenylic Acid)-Containing Rna Of Euglena-Gracilis During Chloroplast Development .2. Transcriptional Origin Of The Different Rna

The transcriptional origin of the polyadenylated RNA has been studied in dark‐grown cultures of Euglena gracilis and during light‐induced chloroplast development. Complementary DNA (cDNA) to poly(A)‐containing RNA from different preparations (isolated chloroplasts and total cell polyribosomes from the wild‐type Z strain or from the aplastidic mutant W 3 BUL) were synthesized and used for hybridization experiments. a) In Euglena cells illuminated for 0, 1 or 24 h, 7–10% of the total cell poly(A)‐containing RNA are transcribed from chloroplast DNA. However, when RNA is extracted from isolated chloroplasts, this proportion of poly(A)‐containing RNA is about two times higher (20%); in this case, the poly(A)‐containing RNA could belong to a specific class and be transcribed from 18–20% of the double‐strand chloroplast DNA. b) In the dark‐grown cultures or in the greening cultures, the major part of the total cell poly(A)‐containing RNA is transcribed from the non‐repetitive sequences of nuclear DNA. The isolated chloroplast preparations contain also a high proportion of poly(A)‐containing RNA from nuclear origin. c) About 10% of the total cell poly(A)‐containing RNA of the wild‐type strain, absent in the poly(A)‐containing RNA of the aplastidic mutant, appear hybridizable to the nuclear genome of this mutant. Thus the transcription of some of the RNA encoded by nuclear DNA could be controlled by the presence of the chloroplast. Moreover, the fact that isolated chloroplast preparations appear to be enriched in such poly(A)‐containing RNA from nuclear origin, suggests that these RNA are located at the level of the chloroplast.