Abstract
Interphase macronuclear chromatin of the ciliate Bursaria truncatella was studied on spread preparations of individual nuclei isolated at different times after vegetative division. During the period from 0.5 to 3 h after cell division most of the macronuclear chromatin was in the decompacted state and had the appearance of loose agglomerations of fibers in regions where transcriptional complexes were observed. The maximum amount of decompacted chromatin was observed 0.5–1.5 h after cell division. At 2–3 h after division the amount of decompacted chromatin decreased as the amount of compact chromatin organized in clumps 0.12–0.18 μm in diameter increased. Macronuclei from cells that had finished growing and differentiating contained practically only linked chromatin clumps. Electron microscopic autoradiography showed that chromatin organized in clumps was transcriptionally inactive. Transcription only took place in decompacted chromatin agglomerations. Characteristic features of the structure of transcriptionally active genes in B. truncatella are described in detail.
Published Version
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