THE CONTROL OF PROTEIN SYNTHESIS IN RABBIT RETICULOCYTE LYSATES

Abstract

This chapter examines the control of protein synthesis in rabbit reticulocyte lysates. Reticulocytes need iron to make globin, and the supply of hemin regulates protein synthesis in these cells. A simple experiment has shown that the inhibition of protein synthesis occurs because of the activation of an inhibitor rather than some initiation factor requiring hemin as an essential cofactor in these particular cells. Subsequent studies showed that the inhibitor was a protein that acted catalytically; one molecule could inhibit over 100 ribosomes. They also defined a pathway of activation of the inhibitor called hemin controlled repressor (HCR) showing that it normally existed as an inactive entity, which could be activated either by incubation at physiological temperature in the absence of hemin or by brief incubation with N-ethylmaleimide or other –SH reactive reagents. At early stages of activation, it can be deactivated by the addition of hemin, but at later stages, hemin has no effect on it.