Chromosome structure and condensation in relation to DNA integrity

Single strand DNA breaks were photo-induced in Chinese hamster chromosomes. An electron microscope analysis indicated dispersion or loss of chromatin, and the linear continuity of the metaphase chromosome was mainly represented by longitudinal chromatin fibres. The degree of chromosome damage was related directly to the photo-exposure, and inversely to the condensation level reached by the chromosome prior to exposure. Photo-irradiation of G2 or early prophase chromatin induced chromosome pulverization. However, if the chromatin had reached the maximum metaphase condensation then DNA breakdown only partially disorganized the chromosome general morphology, suggesting that DNA integrity is a factor in chromosome condensation and structural stability at mitosis.