Structure of the interphase chromatin in the ciliata Bursaria truncatella macronucleus. II. Loop organization of inactive chromatin clumps

Electron microscopic study of chromatin organization in isolated macronuclei of a ciliate Bursaria truncatella showed macronuclear chromatin to be organized in compact clumps 120--180 nm in diameter linked with each other by one or several chromatin fibres. Macronucleus being dispersed in a solution of low ionic strength, radial loops basically of nucleosomal structure start appearing around chromatin clumps. Long-time dispersing of macronuclear chromatin brings complete decompactization of chromatin clumps into a set of nucleosome fibres. The way the fibres of interphase chromatin are packed in a chromatin clump is discussed.