2-mercapto-1-( -4-pyridethyl) benzimidazole, an inhibitor of RNA synthesis: a reevaluation

The effect of 2-mercapto-1-(β-4-pyridethyl) benzimidazole (MPB) was determined in fetal rat liver explants. MPB exerted little effect upon the uptake of ¹⁴C-labeled orotic acid by the fetal liver, but exerted a very pronounced inhibition of the incorporation of the precursor into TCA-insoluble, alkalilabile material. These studies justify in fetal rat liver systems the use of MPB as an inhibitor of RNA synthesis unmediated by permeability effects.