Functions as part of axonemal radial spoke complexes, which play an important part in the motility of sperm and cilia (By similarity). In vitro, does not display nucleoside diphosphate kinase (NDPK) activity (Probable) (PubMed:16313181, PubMed:9742940). Exhibits a 3'-5'-DNA exonuclease activity that removes single nucleotides from the 3' terminus of single-stranded DNA substrates and digests overhanging mismatched 3' termini from double-stranded DNA substrates, possibly participating in DNA nucleolytic processing (PubMed:16313181). Confers protection from cell death mediated by BAX and alters the cellular levels of several antioxidant enzymes, including GPX5 (By similarity). Might be involved in spermiogenesis by enhancing the ability of late-stage spermatids to eliminate reactive oxygen species (By similarity). {ECO:0000250|UniProtKB:Q99MH5, ECO:0000269|PubMed:16313181, ECO:0000305|PubMed:9742940}. This is the function of Ensembl gene identifier ENSG00000112981 (NME5, NME/NM23 family member 5).