Intranuclear anchoring of repetitive DNA sequences: Centromeres, telomeres, and ribosomal DNA

Centromeres, telomeres, and ribosomal gene clusters consist of repetitive D NA sequences. To assess their contributions to the spatial organization of the interphase genome, their interactions with the nucleoskeleton were exam ined in quiescent and activated human lymphocytes. The nucleoskeletons were prepared using "physiological" conditions. The resulting structures were p robed for specific DNA sequences of centromeres, telomeres, and ribosomal g enes by in situ hybridization; the electroeluted DNA fractions were examine d by blot hybridization. In both nonstimulated and stimulated lymphocytes, centromeric alpha-satellite repeats were almost exclusively found in the el uted fraction, while telomeric sequences remained attached to the nucleoske leton. Ribosomal genes showed a transcription-dependent attachment pattern: in unstimulated lymphocytes, transcriptionally inactive ribosomal genes lo cated outside the nucleolus were eluted completely. When comparing transcri ption unit and intergenic spacer, significantly more of the intergenic spac er was removed. In activated lymphocytes, considerable but similar amounts of both rDNA fragments were eluted. The results demonstrate that: (a) the v arious repetitive DNA sequences differ significantly in their intranuclear anchoring, (b) telomeric rather than centromeric DNA sequences form stable attachments to the nucleoskeleton, and (c) different attachment mechanisms might be responsible for the interaction of ribosomal genes with the nucleo skeleton.