Exonuclease VIII of Escherichia coli. II. Mechanism of action.

Exonuclease VIII from Escherichia coli was shown to preferentially degrade linear duplex DNA, although a limited amount of activity with single-stranded linear DNA substrates was detected. No nucleolytic activity was observed with double-stranded circular substrates containing single strand breaks or gaps. Exonuclease VIII was shown to degrade linear duplex DNA from the 5' termini of the molecules and proceed in the 5' to 3' direction via a processive reaction mechanism. Initiation could occur from either a 5'-hydroxyl or 5'-phosphate residue at equal rates. The products of degradation of linear duplex DNA were an equivalent amount of 5'-mononucleotides and single-stranded DNA. Possible roles for exonuclease VIII in genetic recombination are discussed.