We have isolated an enzyme activity from extracts of Escherichia coli that catalyzes the hydrolysis of phospho diester bonds in the single-stranded deoxyribopolymer (dU)[3H]dT)(2000) containing depyrimidinated sites created by enzymatic removal of uracil with uracil-DNA glycosylase. Nondepyrimidinated polymer is not degraded by the enzyme, nor is the depyrimidinated polymer degraded after reduction of apyrimidinic sites with sodium borohydride. The enzyme also degrades circular M13 DNA containing uracil or dena-tured phage PBS2 DNA (which naturally contains uracil) only after the removal of uracil from these substrates by uracil-DNA glycosylase. Undamaged or depurinated duplex PM2 or ColEl DNA and undamaged Ml3 single-stranded DNA are not attacked by the enzyme. The activity sediments in glycerol gradients with a relative s value of 4.2 S and has a Stokes radius of 31 Å, yielding a calculated Mr, ~ 56 000. The fractional ratio (f/f0) is calculated at 1.25. The enzyme hasno requirement for any known cofactors and is insensitive to inhibition by p-(chloromercuri)benzoate. Activity is inhibited in the presence of adenosine 5'-triphosphate (ATP), tRNA or high ionic strength and is slightly stimulated by MnCl2 or CaCl2.
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