Ultrastructure of interphase chromosomes

Abstract

A study of the ultrastructure of interphase chromosomes of frog erythrocytes and human leucocytes suggested that the 500, 250 and 100 Å microfibrils observed in different preparations may represent different orders of coiling of a basic 40-60 Å microfibril. Unlike the situation in lampbrush chromosomes, DNAse digestion did not result in the disruption of microfibril continuity. It seems likely that DNA in a loosely bound DNA-histone complex may be more prone to fragmentation than in a more tightly bound complex. The uncoiling of microfibrils brought about by treatments with 1 M ammonium acetate and trypsin supports Zubay's [23] model involving histones in the supercoiling of DNA.