The initiator tRNA acceptance assay as a short-term test for carcinogens. 1. A standardized procedure

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Abstract
A short-term test for carcinogens has been developed based on the interaction of chemical carcinogens with tRNAFMet in vitro. Transfer RNA from rat or rabbit liver is pre-treated with compounds to be tested in the presence of microsomal enzymes and NADPH. Re-isolated tRNA is then charged with L-methionine by aminoacyl-tRNA synthetases from E. coli B. Carcinogens induce a stimulation of tRNA charging whereas chemically similar non-carcinogenic compounds do not show this effect. Experiments with model substances N-methyl-N''-nitro-N-nitrosoguanidine (strong carcinogen) and aflatoxin G1 (weak carcinogen) revealed some differences in dose effect relationships. It is advisable to test unknown compounds at three different concentrations (10-5, 10-7 and 10-9 mg/ml) with at least two different quantities of microsomal enzymes. Tests on > 150 different compounds performed so far indicate that the evaluation of results as % of stimulation (when compared with the control value obtained with the charging of tRNA treated with the solvent only) may allow a quantitative discrimination between weak and intermediate, and strong carcinogens. The procedure is rapid, well reproducible and relatively inexpensive and may be used to complement the other short-term tests for carcinogenicity.