Radioadapted chicken embryo cells: challenge specificity and alterations in higher-order DNA structure.

Radioadapted chicken embryo cells (X-irradiation in ovo with 10 cGy at the 14th day of development with priming periods of 24 h) were treated in vitro by challenge doses of 14 different DNA- and/or chromatin-interactive agents, including X-rays. A decrease in the cellular damage, as measured by scheduled DNA synthesis, was only observed with X-irradiation. Sedimentation of nucleoids as well as viscosity of alkaline lysates from ethidium bromide (0.35-400 micrograms/ml)-, novobiocin (125-1800 micrograms/ml)-, and hyperthermia (30 min at 43 degrees and 45 degrees)-treated cells suggest a higher tendency of radioadapted cells to undergo positive DNA supercoiling. When DNA from adapted and non-adapted chicken embryo cells was used as substrate, neither its digestion by DNase I nor the inhibition of DNase I activity by various DNA-interactive agents was changed in primed cells. From the previous investigations as well as from the present results it is concluded that an increase of tightening of protein-DNA interactions within the nuclear matrix is a molecular determinant of the elevated radiation resistance in radioadapted chicken embryo cells.