Does the interchromatin compartment contain actin?

Transient blockage of transcription in chick liver by alpha-amanitin results in a temporary clearing of nucleoplasmic regions in affected nuclei and concurrent exposure in situ of a discrete interchromatin framework. This is accompanied by sharp decreases in total nuclear RNA (approximately 28%) and nonhistone protein content (approximately 18%). Electrophoretic analysis of matrix fraction proteins from such highly denuded nuclei shows a marked relative enrichment in actin and RNP-derived polypeptides. These observations suggest that actin is a real constituent of the interchromatin region and supports various reports that this protein may have a basic structural role in nuclei.