Allosteric enzyme-tRNA complexes as regulators of transcription or translation.

The dehydrogenase activity of chorismate mutase-prephenate dehydrogenase, the allosteric enzyme of the tyrosine biosynthetic pathway in Escherichia coli, is inhibited by tRNA. The inhibitory effect of tRNA from E. coli is specific, other RNA species or polynucleotides have no inhibitory effect or only slightly influence the activity of the enzyme. While NAD only slightly influences the inhibitory effect of tRNA from E. coli, prephenic acid at high concentrations suppresses the inhibition. In he presence of a fixed concentration of NAD and low concentration or absence of prephenic acid the inhibitory effect of tRNA is time and temperature dependent. It seems that in the presence of tRNA and low concentration of prephenate the enzyme undergoes a time and temperature dependent conformational change. This process is reversible and can be influenced by the concentration of prephenic acid, the first precursor of the tyrosine biosynthetic pathway. The possible regulatory role of allosteric enzyme-tRNA complexes is discussed.