Effect of hyperthermia on DNA loop-size in HeLa S3 cells.

Nuclear matrices of heated and non-heated HeLa S3 cells were isolated and average DNA loop-sizes were compared. Heat treatment (30 min at 45 degrees C) resulted in an ultimate survival level of the cells of about 10 per cent. The loop-size determinations were done on nuclear material isolated from the cells directly after heat treatment. In the nuclear matrices isolated from the heated cells about 1.8 times more protein was bound as compared to the matrices from control cells. Enzymatic analysis using DNase I digestion, followed by centrifugation on neutral sucrose gradients, was performed. Also, halo visualization was combined with autoradiography. Both methods revealed no gross alterations in DNA loop-sizes. The possible function of DNA loop organization in the effect of hyperthermic interference with DNA-related processes is discussed.