ALTERATIONS IN NUCLEAR MATRIX ULTRASTRUCTURE OF G1-MAMMALIAN CELLS FOLLOWING HEAT-SHOCK - RESINLESS SECTION ELECTRON-MICROSCOPY, BIOCHEMICAL, AND IMMUNOFLUORESCENCE STUDIES

Heat shock is known to inhibit vital nuclear functions associated with DNA and RNA metabolism. It has been proposed that the reported heat-i nduced excess protein accumulation in the nuclear matrix (NM) fraction may alter NM sites crucial for DNA and RNA processing. To test this h ypothesis, we examined the fine structure of the NM in synchronous pop ulations of G1 Chinese hamster ovary cells before and after heating by using the technique of resinless section electron microscopy. Heat di d induce morphological alterations in the NM. The NM of control cells contained a honeycomb-like arrangement of fibers after chromatin remov al. Following heat shock, NMs appeared as more highly anastomosing net works of polymorphic fibers and an overall increase in electron densit y was observed. Residual nucleoli from heated NMs underwent alteration s in distributions of electron density both internally and at their pe ripheries. The increase in electron density observed in heated NMs was accompanied by an increase in protein mass and a relatively smaller i ncrease in RNA mass as indicated by parallel sodium dodecyl sulfate po lyacrylamide gel electrophoresis (SDS PAGE) and isotopic labeling (pro tein/DNA and RNA) studies. Some excess protein accumulation could also be directly localized onto NM fibers by use of antibodies to heteroge neous ribonucleoprotein complex antigens. It is concluded that alterat ions of NM fine structure can reflect the heat-stressed state of the c ell, may account for the heat-induced inhibition of nucleic acid metab olism, and may be useful as an indicator of physiological or pathologi cal stress in general.