[5′-32P]pdT8d(-)dT7, containing an AP (apurinic/apyrimidinic) site in the ninth position, and [d(-)-1′,2′-3H, 5′-32P]DNA, containing AP sites labelled with 3H in the 1′ and 2′ positions of the base-free deoxyribose [d(-)] and with 32P 5′; to this deoxyribose, were used to investigate the yields of the beta-elimination and delta-elimination reactions catalysed by spermine, and also the yield of hydrolysis, by the 3′-phosphatase activity of T4 polynucleotide kinase, of the 3′-phosphate resulting from the beta delta-elimination. Phage-phi X174 RF (replicative form)-I DNA containing AP (apurinic) sites has been repaired in five steps: beta-elimination, delta-elimination, hydrolysis of 3′-phosphate, DNA polymerization and ligation. Spermine, in one experiment, and Escherichia coli formamidopyrimidine: DNA glycosylase, in another experiment, were used to catalyse the first and second steps (beta-elimination and delta-elimination). These repair pathways, involving a delta-elimination step, may be operational not only in E. coli repairing its DNA containing a formamido-pyrimidine lesion, but also in mammalian cells repairing their nuclear DNA containing AP sites.

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