INCREASED CONTRACTILE ACTIVITY DECREASES RNA-PROTEIN INTERACTION IN THE 3'-UTR OF CYTOCHROME-C MESSENGER-RNA

This study was designed to gain an insight into mechanisms by which cy tochrome c gene expression is enhanced by increased contractile activi ty in skeletal muscle. When rat tibialis anterior muscles were stimula ted (10 Hz, 0.25 ms) for 0, 2, 6, 12, or 24 h or 2, 5, 9, or 13 days ( n = 4 for each time point), cytochrome c protein (enzyme-linked immuno sorbent assay) and mRNA (Northern blot analysis) concentrations starte d to increase by 9 days, and this was associated with concurrent decre ases in cytochrome c mRNA-protein interaction (RNA gel mobility shift assay). We found that the decreased RNA-protein interaction in the sti mulated muscle extract was restored by ultracentrifugation (150,000 g, 1 h) in the supernatant fraction. The 150,000 g pellet fraction of st imulated muscle was capable of inhibiting the RNA-protein interaction in control tibialis anterior muscles. These results provide evidence o f an inhibitory factor that is responsible for decreasing RNA-protein interaction in the 3'-untranslated region of cytochrome c mRNA in cont inuously stimulated muscle.