A Plant 3′-Phosphoesterase Involved in the Repair of DNA Strand Breaks Generated by Oxidative Damage

Two novel, structurally and functionally distinct phosphatases have been identified through the functional complementation, by maize cDNAs, of an Escherichia colidiphosphonucleoside phosphatase mutant strain. The first, ZmDP1, is a classical Mg2+-dependent and Li+-sensitive diphosphonucleoside phosphatase that dephosphorylates both 3′-phosphoadenosine 5′-phosphate (3′-PAP) and 2′-PAP without any discrimination between the 3′- and 2′-positions. The other, ZmDP2, is a distinct phosphatase that also catalyzes diphosphonucleoside dephosphorylation, but with a 12-fold lower Li+ sensitivity, a strong preference for 3′-PAP, and the unique ability to utilize double-stranded DNA molecules with 3′-phosphate- or 3′-phosphoglycolate-blocking groups as substrates. Importantly, ZmDP2, but not ZmDP1, conferred resistance to a DNA repairdeficient E. coli strain against oxidative DNA-damaging agents generating 3′-phosphate- or 3′-phosphoglycolate-blocked single strand breaks. ZmDP2 shares a partial amino acid sequence similarity with a recently identified human polynucleotide kinase 3′-phosphatase that is thought to be involved in DNA repair, but is devoid of 5′-kinase activity. ZmDP2 is the first DNA 3′-phosphoesterase thus far identified in plants capable of converting 3′-blocked termini into priming sites for reparative DNA polymerization.