Organic Photochemistry of Nucleic Acids*

Abstract

Summary Starting with the isolation of thymine dimer derived from DNA of u.v.‐irradiated bacteria, a systematic investigation was begun from which it was concluded that the basis for the action of u.v.‐light is a photochemical dimerization. Depending on the dose of u.v.‐light and the conditions for hydrolysis of DNA and isolation procedures, other photoproducts of thymine were isolated. Experimental data for the conversion of cytosine to uracil are presented. By use of monochromatic u.v.‐light we could demonstrate that only intrastrand dimerization occurs. The radiation chemical behavior of uracil and cytosine was investigated with tritium labeled compounds. The mechanism for the various kinds of sensitization with 5‐halogen‐uracils, with dyes (thiopyronin, methylene blue, and pyronin) with carcinogenic hydrocarbons and with furocoumarins, which parallels partly the photochemical degradation of guanine is discussed. U.V.‐inactivated bacteria and polyuridylic acid are reactivated better by irradiation with visible light when hydrogen peroxide or uranyl acetate are present. The mechanism of this reaction is discussed. The absence of the α, β‐unsaturated double bond could be expected to protect the thymine molecule from dimerization; after incorporation of azathymine into the DNA, bacteria do indeed exhibit u.v.‐resistance. Moreover, after treatment of bacteria with hydrogen peroxide and visible light, by which the 5,6 double bond in the thymine and cytosine molecules is also attacked, bacteria become u.v.‐resistant. The specific alteration of uracil and cytosine by u.v.‐irradiation and of guanine through photodynamic action can be used as a simple method for sequence analysis of protein codons. It is also of use in determining the interaction between messenger‐RNA, transfer‐RNA and ribosomes during protein synthesis.

Thiopyronine-sensitized Photodynamic Inactivation of RNA Synthesisin Vitro

“…The inactivation of the template in the absence of light is probably due to a steric hinderance of the polymerase caused by an outside binding of TP on the denaturated DNA (Micheler 1972) . In accordance with the findings from various other dyes, the aromatic amino-acids histidine, tyrosine and methionine are photo-oxidized on illumination in the presence of TP (Wacker, Dellweg, Trager, Kornhauser, Lodemann, Turck, Selzer, Chandra and Ishimoto 1964) . Because there is no notable inhibition of the binding and initiation capacity of the polymerase, it is probable that photodynamic inactivation with the doses used here did not primarily destroy such amino-acid residues which are necessary for the maintenance of the natural conformation of the polymerase .…”

Pyrimidine Photodimers

“…Direct Irradiation i. URACIL. During the course of an irradiation, the amount of dimer increases with increasing exposure to an equilibrium level, then declines as Ura is converted to other products (Wacker et al, 1964). (1958), Beukers et al (1959a), and Beukers and Berends (1961) demonstrated that Ura un-dergoes photochemical reactions suggestive of dimerization.…”

“…The photodimerization of Urd in aqueous solution has been demonstrated using radioactive label and by separating products by paper chromatography (Wacker et al, 1961b). URIDINE.…”

“…For example, the following sensitizers have been used: uranyl acetate (Wacker et al, 1964), 2,6-naphthalenedisulfonate and 2-triphenylene sulfonate (Lamola, 1966), chloranil ), a number of anthraquinonesulfonates (Ben-Hur and , and indole derivatives such as tryptophan (Hélène and Charlier, 1971;Charlier and Hélène, 1975). For example, the following sensitizers have been used: uranyl acetate (Wacker et al, 1964), 2,6-naphthalenedisulfonate and 2-triphenylene sulfonate (Lamola, 1966), chloranil ), a number of anthraquinonesulfonates (Ben-Hur and , and indole derivatives such as tryptophan (Hélène and Charlier, 1971;Charlier and Hélène, 1975).…”

Investigation of molecular mechanisms in photodynamic action and radiobiology with nanosecond flash photolysis and pulse radiolysis. Progress report, July 1, 1973--June 30, 1974

“…It has been found that a surprising variety of sensitizers are active, including uranyl oxalate (Wacker, et al, 1964), anthraquinone derivatives (Ben-Hur and Rosenthal, 1970), chloranil (Rosenthal and Elad, 1968), naphtho-imidazoles and arylsulfonic acids, such as 3-benzophenonesulfonic acid, (Lamola, 1966), and indole derivatives (Helene and Charlier, 1971). The active indole derivatives such as tryptophan are known to be electron donating in the excited state and may cleave by a process paralleling e in reaction (1).…”