Chemical Modification of Nucleic Acids and Related Substances with a Carcinogen Ptaquiloside.

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Studies on chemical modification of nucleic acids and related substances with a bracken carcinogen ptaquiloside 1__- have been made. Ptaquiloside 1__- was isolated from the plant material and was converted with alkali to the ultimate carcinogen dienone 2__-.1. Chemical Modification of Nucleosides, Nucleotides, and DNA with Dienone 2__-. Four nucleosides and two nucleotides reacted with dienone 2__- to give alkylated products. Alkylation took place at: (1) the N^6 position in adenosine; (2) the O^6 and N-7 positions in guanosine; (3) the N-3 and O^4 positions in uridine; and (4) the N-3 position in cytidine. Alkylation occurred at the phosphate group in 5'-AMP or 5'-GMP. An adduct formed between salmon sperm DNA and dienone 2__- was thermally hydrolyzed to afford the N-3 alkylated adenine and the N-7 alkylated guanine as major. products.2. Base-specific Cleavage of DNA Dienone 2__-. DNA cleaving activity of dienone 2__- was detected by the topological change of plasmid pBR322 DNA by virtue of gel electrophoresis. Base specificity in the cleavage of DNA with dienone 2__- was examined using DNA fragments end-labeled with ^<32>P. The 3'- or 5'-labeled double-stranded DNA fragments modified with dienone 2__- were heated (condition-A: 90゜C, 3min) or heated in the presence of piperidine (condition-B: 90゜C, 30 min) and the products were analyzed by gel electrophoresis. Whereas the DNA strand scission took place solely at the 3' side of deoxyadenosine residue of the DNA fragments under the condition-A, the guanine-specific cleavage of the DNA fragments occurred under the condition-B. The cleavage of the single-stranded DNA fragments occurred at both adenine and guanine sites under the condition-A and at the guanine site under the condition-B. Thus the features of the modification and cleavage of DNA with dienone 2__- have been disclosed.