Protein-depleted chromosomes. I. Structure of isolated protein-depleted chromosomes.

Protein-depleted isolated Chinese hamster chromosomes have been obtained by different protein extraction procedures and examined by electron microscopy and SDS-polyacrylamide gel electrophoresis. Salt-resistant centromeric and telomeric structures are visible in protein-depleted chromosomes and the protein-depleted chromosomes appear to have a regular, longitudinal pattern in critical point dried preparations. The scaffold-like structure of protein-depleted chromosomes is highly affected by the ionic strength and composition of the extraction medium and by the spreading conditions. Nucleosomal histones of isolated chromosomes proved to be more sensitive to the sodium chloride treatment than histones of isolated chromatin. A small, but constant quantity of core histones was detected in 2 M salt extracted chromosomes and H3 and H4 histones of isolated chromosomes appeared to be resistant to the sodium deoxycholate treatment.