Effect of 7,12-dimethylbenz(a)anthracene on the binding of aminoacyl transfer RNA in rat liver

Homogenates of the liver of female rats obtained 2 or 7 days or 3 months after the i.v. injection of 7,12-dimethylbenz(a)anthracene were used to prepare ribosomes and postmicrosomal supernatant fractions and to prepare 0.5 M KCl salt wash fractions of the 40 S ribosomal subunits. The activity of the ribosomes was unchanged by 7,12-dimethylbenz(a)anthracene. The activity of the supernatant preparation, which contained limiting amounts of Elongation Factor 1 relative to Elongation Factor 2, in peptide synthesis was significantly increased 2 days not 7 days after the injection. Evidence was obtained that this increase was due to increased activity in binding phenylalanyl transfer RNA. The factor-dependent binding of methionyl transfer RNAfMet to control rat liver ribosomes was also markedly increased 2 days but not 7 days after the injection. The liver of animals that bore mammary tumors 3 months after 7,12-dimethylbenz(a)anthracene injection also showed an increase in binding both of the aminoacyl transfer RNA species. The results are discussed in relation to the induction of liver drug-metabolizing enzymes and to liver regeneration.