To elucidate the biological roles of mono-ubiquitinated annexin A1 in nuclei, we investigated the interaction of purified nuclear mono-ubiquitinated annexin A1 with intact and oxidatively damaged DNA. We synthesized the 80mer 5′-GTCCACTATTAAAGAACGTGGACTCCAACGTCAAAGGGCGAAAAACCGTCTATCAGGGCGATGGCCCACTACGTGAACCA-3′ (P0G), and four additional 80mers, each with a selected single G in position 14, 30, 37 or 48 replaced by 8-oxo-guanosine (8-oxo-G) to model DNA damaged at a specific site by oxidation. Nuclear mono-ubiquitinated annexin A1 was able to bind oligonucleotides containing 8-oxo-G at specific positions, and able to anneal damaged oligonucleotide DNA to M13mp18 in the presence of Ca2+ or heavy metals such as As3+ and Cr6+. M13mp18/8-oxo-G-oligonucleotide duplexes were unwound by nuclear annexin A1 in the presence of Mg2+ and ATP. The binding affinity of nuclear annexin A1 for ssDNA was higher for oxidatively damaged oligonucleotides than for the undamaged oligonucleotide P0G, whereas the maximal binding was not significantly changed. The carcinogenic heavy metals, As3+ and Cr6+, increased the affinity of mono-ubiquitinated annexin A1 for oxidatively damaged oligonucleotides. Nuclear mono-ubiquitinated annexin A1 stimulated translesion DNA synthesis by Pol β. Nuclear extracts of L5178Y tk(+/−) lymphoma cells also promoted translesion DNA synthesis in the presence of the heavy metals As3+ and Cr6+. This DNA synthesis was inhibited by anti-annexin A1 antibody. These observations do not prove but provide strong evidence for the hypothesis that nuclear mono-ubiquitinated annexin A1 is involved in heavy metal promoted translesion DNA synthesis, thereby exhibiting the capacity to increase the introduction of mutations into DNA.