Effect of 7,12-Dimethylbenz(a)anthracene on the Binding of Aminoacyl Transfer RNA in Rat Liver1

of mRNAand also upon factors that could be removed by procedures involving a 0.5 M KCI wash (3). Furthermore, there was an increased capacity for protein synthesis bo cated in the supernatant fraction (i.e. , the cytosol), which contains the bulk of the elongation factors required for protein synthesis (2, 4, 13). The increased activity of the supernatant fraction, which contains an excess of Ebonga tion Factor 2 relative to Elongation Factor 1, was due to an increased reactivity of Elongation Factor 1, which binds aminoacyb-tRNA to nibosomes (32, 36, 51). In addition to these observations of increased elongation factor activity during liver enzyme induction by DDT, which is carcinogenic in liver (46), there are reports of increased initiation factor activity in liver following the administration of the carcinogen 3-methybcholanthreneand also in trans plantabbe liver tumors (20, 30, 31). The potent mammary carcinogen DMBA (21) is capable of inducing aromatic arybhydroxylases in liver and mam mary gland , although the metabolism of DMBA apparently differs in these 2 tissues (45). Apparently, DDT inhibits tumor development as well as the toxic effects of DMBA (39, 47). When DMBA is administered during liver regenera tion, it can induce malignant and premalignant changes in the liver itself (29). We have recently found that during the regenerationof liver there is not only an increase in amino acyl-tRNA binding capacity but also an increase in initiation factor activity, as measured by the capacity for methionyl tRNA@eI binding (32). Thus it was important to see whether a non-target tissue of DMBA (i.e. , normal liver) was involved in a similar response to a target tissue (i.e. , regenerating liver or mammary gland) following administration of DMBA. The present experiments describe the effect on normal liver.