Evidence has been obtained that a specific isomer of a diol epoxide derivative of benzo(a)pyrene, (+/-)-7 beta,8alpha-dihydroxy-9alpha, 10alpha-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene, is an intermediate in the binding of benzo(a)pyrene to RNA in cultured bovine bronchial mucosa. An adduct is formed between position 10 of this derivative and the 2-amino group of guanine.

Inclusion of the higher order coupling term in eq 3' is not justified in this system. It appears to contribute less than 1 % to the values of T,.(1 1) These are average internuclear separations, r,, and are related to the equilibrium values, re, by r, = re -I-( Az) where ( Az) is the anharmonicity correction.

The covalent binding of benzo[a]pyrene 4,5-oxide and benzo[a]pyrene-7,8-dihydrodiol 9,10-oxide isomer I and isomer II to nucleic acids in aqueous acetone solution has been investigated. Benzo[a]pyrene 4,5-oxide reacted preferentially with guanosine residues. On the other hand, benzo[a]pyrene-7,8-dihydrodiol 9,10-oxide isomer I and II reacted extensively with guanosine, adenosine, and cytidine residues. Time course studies showed that the reactivity of isomer I or isomer II with homopolyribonucleotides followed the order poly(G) greater than poly(A) greater than poly(C). Alkaline or enzymatic hydrolysis of the modified nucleic acids and subsequent chromatography on Sephadex LH-20 columns yielded benzo[a]pyrene-nucleotide adducts. These were enzymatically converted to the corresponding nucleosides which were resolved into several distinct components by high-pressure liquid chromatography. Evidence was obtained for the presence of multiple nucleoside adducts of guanosine, adenosine, cytidine, deoxyguanosine, deoxyadenosine, and deoxycytidine. The HPLC profiles of adducts formed with isomer I were different from the corresponding profiles of adducts formed with isomer II. Structural aspects of these nucleoside adducts are discussed.

Calf and beef liver tRNAphe were obtained by fractionation of calf and beef tRNA on BD-cellulose columns and selected regions were further purified by hydroxylapatite chromatography. The tRNAphe was then incubated at pH to the following abbreviations: structure A: imGua (for l,.V--isopropeno-3-methylguanine); structure B: Y-imGua (it so happens that the branched butyrate side chain looks like the letter Y, and hence the original letter can be retained as a modifier), The respective nucleosides become imG and Y-imG while the peroxy compound, IT, is represented by HOs-Y-imGua.

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