We propose that basically three nuclear compartments exist, an &quot;open&quot; higher-order chromatin compartment with chromatin domains containing active genes, a &quot;closed&quot; chromatin compartment comprising inactive genes, and an interchromatin domain (ICD) compartment (Cremer et al., 1993; Zirbel et al., 1993) that contains macromolecular complexes for transcription, splicing, DNA replication, and repair. Genes in &quot;open,&quot; but not in &quot;closed&quot; higher-order chromatin compartments have access to transcription and splicing complexes located in the ICD compartment.