Effect of alkali chlorides on human chromosomes studied by the method of poly-L-lysine binding.

Human metaphase chromosomes A1 and A3 did bind more tritiated poly-L-lysine ([3H]PL) when they were isolated from lymphocyte cultures treated with LiCl rather than with NaCl or KCl. A2 chromosome did not show this differential behavior and in all three cases did bind more [3H]PL than the control A2 chromosome. The effect was dependent on the time of exposure of cells to the salts in tissue culture and on the degree of chromosomal contraction. The observed differences in [3H]PL binding are probably due to differences in surface morphology of the three chromosomes caused by treatment with alkali metal salts.

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.