Factors influencing the binding of n-2-fluorenylacetamide to specific regions of the hepatic genome in vivo in rats

The initial binding of N-fluorenylacetamide (2- FAA) and its N-hydroxy metabolite N-hydroxy-N-2-fluorenylacet- amide (N-OH-2-FAA) within the hepatic genome and the effect of ingestion of a 2-FAA-containing (0.05% wt/wt) diet on this binding were examined in the male noninbred Sprague-Dawley rat. Ingestion of 2-FAA for 2 weeks reduced the amount of newly bound carcinogen up to 80%. The extent of this decrease was significantly greater in rats treated with a single injection of 2- FAA when compared to one of N-OH-2-FAA. The distribution of carcinogen within the genome was measured after fractionation of chromatin by DNase II digestion followed by selective MgCl₂ precipitation. Two hours after a single injection of N-OH-2-FAA, the amount of carcinogen bound per milligram DNA in the presumed template-active chromatin fraction was 16 times that bound to DNA of the presumed template-repressed chromatin fraction. The amount bound to DNA in the nuclease-resistant chromatin was equal to that observed in the DNA of the presumed template-active fraction. Most (85%) of the total bound carcinogen was located on less than 25% of the total DNA. Evaluation of the amount of carcinogen bound to the N-2 or C-8 positions of guanine demonstrated a significant inverse correlation between the amount bound to a DNA fragment and the percent of that binding occurring at the N-2 position. DNA of the repressed chromatin fraction had the largest N-2/C-8 ratio when compared to the ratios seen in both the expressed chromatin and nuclease-resistant chromatin DNA. Pretreatment of rats with 2- FAA when compared to one of N-OH-2-FAA. The distribution of carcinogen within the genome was measured after fractionation of 66.