dietary administration of the hepatocarcinogen 2-acetylaminofluorene ( 2-aaf ) to rats results in the formation of a major hepatic dna adduct , n-(deoxyguanosin-8-yl)-2-aminofluorene ( dg - c8-af ) . in liver dna , 
 dg - c8-af reaches steady - state conditions after approximately 2 weeks of feeding and is removed in a biphasic manner . in these experiments , we have quantified adduct concentrations in a 370 base - pair repetitive dna fragment to determine if the adduct levels and kinetics of adduct removal were similar to those found in total genomic dna . 
 male f344 rats were fed 0.02% 2-aaf for 28 days and were sacrificed at intermittent times up to 56 days after being returned to the control diet . 
 hepatic dna adduct levels were measured by 32p - postlabeling or radioimmunoassay ( ria ) in total genomic dna and in a 370 base - pair fragment obtained by digesting genomic dna with hind iii . 
 biphasic removal of dg - c8-af , which composed about 90% of the total adducts measured , was observed in total genomic dna , with comparable rate constants being detected by both 32p - postlabeling and ria . 
 32p - postlabeling also showed analogous biphasic removal of dg - c8-af in the 370 base - pair fragment . 
 a second adduct , 3-(deoxyguanosin - n2-yl)-2-aaf ( dg - n2-aaf ) , which accounted for about 10% of the total adducts measured , showed similar biphasic removal kinetics in the total genomic dna and the 370 base - pair fragment ; however , as compared to dg - c8-af , little removal of dg - n2-aaf was observed during the slow phase.imagesfigure 2 .