[Characteristics of chromatin structural organization in somatic nucleus of the ciliate Didinium nasutum].

Structural organization of macronuclear chromatin of the ciliate Didinium nasutum was studied. Macronuclear genome of D. nasutum is represented by DNA molecules of subchromosomal size. At interphase, macronuclear chromatin is organized into chromatin clumps approximately 100-200 nm in size and some of them form short thick fibres consisting of several chromatin clumps. Using differential staining of nucleic acids on ultrathin sections we revealed perichromatin fibres and granules on the surface of many chromatin clumps. 3D models of spatial distribution of chromatin clumps in the macronucleus were reconstructed on the basis of serial ultrathin sections and peculiar features of their organization were studied.