INFLUENCE OF THYROID-HORMONE ON ADP-RIBOSYLATION OF NUCLEAR PROTEINS IN CULTURED GH1 CELLS

We present evidence that T3 can alter the ADP-ribosylation of chromatin associated proteins. Nuclei from GH1 cells were incubated with [adenylate-P-32]NAD and the radioactivity incorporated into histone and non-histone proteins was quantitated and analyzed by gel electrophoresis and autoradiography. Incubation of GH1 cells for 24 h with T3 lowered by 40-70% the [P-32]ADP-ribose incorporated into nuclear proteins. However, incubation for 3 h with T3 resulted in a stimulation instead of a decrease of in vitro [P-32]ADP-ribose incorporation. The major ADP-ribosylated component electrophoresed as a 120 000 molecular mass non-histone protein, and radiolabeled histones were also observed. The same protein species were observed for all the experimental groups and T3 affected the extent of ADP-ribosylation but did not alter the sedimentation of the [P-32]ADP-ribosylated components excised from chromatin after micrococcal nuclease digestion.