Alterations in the Nuclear Matrix Protein Mass Correlate with Heat-induced Inhibition of DNA Single-strand-break Repair

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Abstract
The total protein mass co-isolating with the nuclear matrix or nucleoid from Chinese hamster ovary (CHO) cells was observed to increase in heated cells as a function of increasing exposure temperature between 43.degree. C and 45.degree. C or of exposure time at any temperature. The sedimentation distance of the CHO cell nucleoid in sucrose gradients increased with increasing exposure time at 45.degree. C. Both these nuclear alterations correlated in a log-linear manner with heat-induced inhibition of DNA strand break repair. A two-fold threshold increase in nuclear matrix protein mass preceded any substantial inhibition of repair of DNA single-strand breaks. When preheated cells (45.degree. C for 15 min) were incubated at 37.degree. C the nuclear matrix protein mass and nucleoid sedimentation recovered with a half-time of about 5 h, while DNA single-strand-break repair recovered with a half-time of about 2 h. When preheated cells were placed at 41.degree. C (step-down heating; SDH) a further increase was observed in the nuclear matrix protein mass and the half-time of DNA strand break repair, while nucleoid sedimentation recovered toward control values. These results implicate alterations in the protein mass of the nuclear matrix in heat-induced inhibition of repair of DNA single-strand breaks.