STRUCTURAL-CHANGES OF CHROMATIN DURING ACTIVATION OF PROTOONCOGENES BY CYCLOHEXIMIDE - DOSE-EFFECT RELATIONSHIP

Expression of cellular protooncogenes c-myc and c-fos in rat liver was studied with varied rates of protein synthesis (i.e., doses of cycloh eximide). Activation of the protooncogenes begins at approximately 50% inhibition of nuclear protein synthesis. This is associated with prof ound structural reorganization of chromatin manifested by decreased cl eavage of chromatin by Ca2+,Mg2+-DNase and increased general condensat ion of chromatin. Topoisomerase II may play a role in the conformation al transitions of chromatin occurring during activation of protooncoge nes.