Enzymatic joining of DNA strands: a novel reaction of diphosphopyridine nucleotide.

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Abstract
Covalent joining of DNA strands catalyzed by an enzyme from Escherichia coli. requires: DPN as cofactor; a 5[image]-phos-phoryl terminus on the DNA; and 5[image]-and3[image]-DNA termini in H-bonded juxtaposition. The strands become joined through a 3[image]-5[image]-phospho-diester bond, while the DPN is cleaved to AMP and NMN [nicotinamide mononucleotide]. The reaction mechanism might involve formation of a pyrophosphoryl bond between 1/2 of DPN (either AMP or NMN) and the 5[image]-terminal phosphoryl group of the DNA with subsequent nucleo-philic attack on this linkage by the 3[image]-terminal OH group of the juxtaposed DNA strand. Since the related enzyme from T4-infected cells uses ATP as cofactor, a common mechanism may involve the intermediate formation of an adenylyl-5[image]-phosphoryl terminus on the DNA.