Metabolic turnover of proliferation-related nuclear proteins in serum-stimulated Swiss mouse 3T3 cells

Abstract

Stimulation of quiescent Swiss mouse 3T3 cells either by serum or by pure growth factors induces DNA synthesis after a lag period of about 15 h. Following restimulation by serum or by growth factors there is an overall increase of 2–4-fold in the rate of biosynthesis of nuclear proteins. Two nuclear polypeptides show specific temporal correlations with the transition from quiescence to proliferation. The synthesis of p30 (30 kDa, p I 5.2) is at a maximum within 5 h of restimulation, while the synthesis of p36 (36 kDa, p I 4.25) is first seen at 10–12 h after restimulation. The synthesis of p36 correlates well with the initiation of DNA biosynthesis. The metabolic turnover of both of these proteins has been estimated by pulse-chase and by cycloheximide inhibition experiments. They both have a half-life of 10–15 h and appear to be cell-cycle related.