Possible correlations between post-heat alterations in nuclear protein mass and the resumption of macromolecular (DNA, RNA, and protein) synthesis were investigated in CHO cells. Nuclear protein content was measured using flow cytometry. Macromolecular synthesis was measured by incorporation of radioactively labeled precursors into TCA-precipitable material of whole cells and isolated nuclei. Following an initial increase which was dependent on the heat dose, nuclear protein mass decreased following a monotonic function which appeared to be multiphasic. The synthesis of DNA, RNA, and protein was inhibited in a manner dependent on the heat dose and remained suppressed for an interval dependent on the heat dose before recovery. The kinetics of resumption of DNA, RNA, and protein synthesis correlated linearly with the nuclear protein mass measured immediately after heating. Also, the time of onset of recovery of RNA and protein syntheses correlated linearly with the time at which nuclear protein mass returned to 125% of control, a level which has been implicated as a possible threshold in previous studies. More significantly, the onset of the resumption of DNA synthesis showed a one-to-one correlation with the time at which the nuclear protein mass returned to 125% of control. These correlations suggest that there may be causal relationships between the resumption of DNA, RNA, and protein synthesis and the reduction of the amount of nuclear protein binding, particularly in the case of DNA synthesis.

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