Chromosome Breakage by Deoxyribonuclease

THE possibility that endogenous deoxyribonuclease might play a part in inducing chromatid breakage was suggested by our experiments describing a high incidence of chromosome breaks and rearrangements in human diploid cell strains after selective damage to lysosomes 1 . We describe here a similar effect when exogenous deoxyribonuclease is introduced into cells in the presence of hypertonic MgSO 4 . This is a modification of the method used by Wecker 2 in assays of the infectivity of extracted viral nucleic acid.