Influence of Heat on the Chromatin Structure in HeLa Nuclei

HeLa cells were heated at 45°C for 30 min, their nuclei were removed, and their chromatin was digested with either micrococcal nuclease or DNase I. Comparison with results from unheated cells that were handled similarly indicated that no change in the basic chromatin structure occurred after heating. The types and quantities of the proteins released from the internucleosomal and core region of the chromatin from heated cells were identical to those released from unheated cells. Most of the additional protein bound in the nucleus during heating appeared to be located with a structure, the nucleoskeleton, comprising the nuclear matrix, nuclear envelope, and its associated DNA. Although the exact nature and location of the additional protein are still unknown, we suggest that even small quantities of any protein located near or at the DNA-nuclear matrix and/or DNA-nuclear envelope attachment sites could be very critical for maintaining the functional and reproductive integrity of a cell with or without subsequent damage from other cytotoxic agents.