[Structure of the interphase chromatin in Bursaria truncatella macronucleus. I. Electron microscopic and autoradiographic study of the structural chromatin changes during differentiation and growth after division].

The structure of interphase chromatin from isolated individual macronuclei of Bursaria truncatella was studied at different moments after cell division. During the period 0,5-3 hours after division most of the macronuclear chromatin is represented by loose agglomerations of decondensed chromatin, where transcription complexes can be seen. The maximum quantity of decondensed chromatin is observed 0,5-1,5 hours after cell division. During the period 1,5-3 hours after the division the part of decondensed chromatin decreases along with the increase of the quantity of dense chromatin organized in chromatin clumps 0,12-0,18 mu in diameter. In completely developed vegetative cells nearly all the chromatin has the structure of closely packed chromatin clumps. Electronmicroscopic autoradiography data show that chromatin clumps are transcriptionally inert, whereas all the transcription processes take place in decondensed chromatin agglomerations. The structure of transcription complexes of B. truncatella macronucleus is discussed in detail.