Protein chain initiation in vitro by liver cell components from DMNA-treated rats

Abstract The mechanism of inhibition of protein synthesis in rat liver after dimethyl-nitrosamine (DMNA) administration was studied at the level of peptide-chain initiation by use of initiation-dependent amino acid incorporating systems. Ribosomal monomers, poly(A)-containing RNA from monosemes and polysemes, and crude initiation factors from microsomes were prepared 2 h after a single dose of DMNA (75 mg/kg), and their activities in the production of new protein chains determined under conditions of nearly linear response. Monosomes and crude initiation factors from DMNA-treated rats were at least as active as those from controls. Preparations of poly(A)-containing RNA had a consistently higher template activity when prepared from polysomes instead of monosomes. However, in neither case was there any loss of activity due to the DMNA treatment. The poly(A)-containing RNA was methylated by DMNA to about the same extent as the 18S and 28S rRNA. The methylation was consistently somewhat higher in the RNA preparations from monosomes than in those from polysomes.