Cytochemical and autoradiographic study of the nucleus of a symbiotic dinoflagellate

SUMMARYNon-nucleolar ribonucleoprotein (RNP) particles, extended chromatin, and the distribution of very active sites of transcription are studied in a dinoflagellate symbiont of sea anemones. A preferential staining method for RNP demonstrates granules 47 ± l0nm (standard deviation) in diameter, partially surrounded by a clear halo, and fibres of different thickness. All these particles are sensitive to RNase. Phosphotungstic acid staining for chromatin shows loops of extended chromatin formed by filaments about 7.5 ±3 nm thick protruding from chromosomes. These filaments are sensitive to DNase. Short labelings with tritiated uridine demonstrate a thin perichromosomal region of high transcriptional activity, which may be the functional equivalent to the perichromatin region of higher eukaryotes. In contrast to the eukaryotic perichromatin region, the perichromosomal zone of dinoflagellates has no feature allowing its morphological characterization. A network of filaments 4 ±2nm thick, resistant to RNase ...