KINETICS OF PHOTOCHEMICAL ADDITION OF [35S]CYSTEINE TO POLYNUCLEOTIDES AND NUCLEIC ACIDS

[35S]Cysteine was ultraviolet irradiated in the presence of poly rU, poly rU:rA, poly rA, poly rC, poly dC, poly dC:dG, poly dT, poly dA:dT, poly dAT :dAT, ribonucleic acid (RNA), or deoxyribonucleic acid (DNA), and the rate constants for the uptake of cysteine per dose of ultraviolet light were tabulated. Whether the polymers were single or double stranded (and/or protonated) had a profound effect upon the reaction rate. Preliminary experiments indicate that tyrosine and serine also add photochemically to DNA but threonine and methionine appear unreactive under the conditions used. These photochemical reactions may provide the mechanism by which DNA and protein are crosslinked in vivo when cells are irradiated with ultraviolet light. © 1968, American Chemical Society. All rights reserved.