The fragile site at 16q22, distamycin A, and the normal pachytene structure of chromosome 16: some possible interrelationships.

It is possible to interpret the fragile site at 16q22 as an exaggerated expression of normal structure observed at pachytene, and to interpret the potential for such expression as a heritable trait. Exposure of cells from affected individuals to distamycin A in vitro may function to facilitate realization of this potential where the trait is not expressed spontaneously.

Labeling and other effects of actinomycin D on human chromosomes.

(3)H-actinomycin D, a guanine-binding agent, labels fixed human chromosomes nonrandomly. Actinomycin D added in G2 inhibits secondary constrictions and breaks chromosomes. There is some tendency for label to be concentrated at the ends of chromosomes and near the centromere. Labeling with (3)H-thymidine in the late stage of DNA synthesis shows a different pattern and in general lacks the telomeric concentrations. The sites of actinomycin D-induced breaks do not show good correspondence with the sites of actinomycin D label.