Synthesis and stability of nuclear matrix proteins in resting and serum-stimulated Swiss 3T3 cells.

The major [35S]methionine-radiolabeled nuclear matrix proteins of mouse 3T3 cells were isolated, and most of these were found to be similar in molecular weight, charge, and protease fingerprint to the nuclear matrix proteins of African green monkey kidney cells, which are found tightly bound to simian virus 40 chromosomes. These nuclear matrix proteins were found to be synthesized in quiescent and serum-stimulated cells and to be turned over slowly during pulse-chase experiments. In contrast, a 70-Kd (kilodalton) neutral protein identified as lamin a was found to be turned over rapidly, producing a 68-Kd protein with a similar isoelectric point. In addition, we observed a decrease in the amounts of two chromatin-bound matrix proteins and a relative increase in lamin a following labeling in the presence of 2 micrograms/ml actinomycin D. However, these effects do not appear to be a result of inhibition of transcription, since they were not observed with other inhibitors (alpha-amanitin and 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole).