Some properties of a partially purified inhibitor(s) of protein synthesis from rat-liver mitochondria.

Abstract

We have previously described an inactive inhibitor of protein synthesis from rat liver mitochondria and its activation by brief incubation with N-ethylmaleimide [Wu, J. M. and Ibrahim, N.G. (1980) FEBS Lett. 119, 25-28]. To study the mode of action of the mitochondrial translational inhibitor (MTI), the relative distribution of monosomes and polysomes in rabbit reticulocyte lysates has been analysed by sucrose gradient centrifugation. These studies show that MTI causes a significant decrease in the amount of polysomes with marginal effect on the polysome profile. Under identical experimental conditions, addition of partially purified heme-regulated inhibitor results in a complete disaggregation of polysomes. Studies with micrococcal-nuclease-treated rabbit reticulocyte lysates suggest that the primary target of MTI is the inactivation of globin mRNA with relatively little effect on other components of the translational machinery. The inhibitor also degrades poly(U), vesicular stomatis virus mRNA, reovirus mRNA, but appears to be inactive against poly(A), Escherichia coli 16S rRNA, HeLa cell rRNA or chick embryo DNA. Chromatography of MTI on heparin-agarose results in the resolution of at least two inhibitory activities. The first inhibitory activity (eluted with 250 mM KCl) can be reversed (50-70%) with high concentrations of glucose 6-phosphate or MgGTP (0.7 mM or 3.3 mM) whereas the second inhibitory activity can only be partially reversed with poly(A)-rich RNA.