5'-3' DNA helicase involved in DNA damage response by acting as an inhibitor of DNA end resection (PubMed:25617833, PubMed:26774285). Recruitment to single-stranded DNA (ssDNA) following DNA damage leads to inhibit the nucleases catalyzing resection, such as EXO1, BLM and DNA2, possibly via the 5'-3' ssDNA translocase activity of HELB (PubMed:26774285). As cells approach S phase, DNA end resection is promoted by the nuclear export of HELB following phosphorylation (PubMed:26774285). Acts independently of TP53BP1 (PubMed:26774285). Unwinds duplex DNA with 5'-3' polarity. Has single-strand DNA-dependent ATPase and DNA helicase activities. Prefers ATP and dATP as substrates (PubMed:12181327). During S phase, may facilitate cellular recovery from replication stress (PubMed:22194613). ATP + H2O = ADP + H(+) + phosphate Inhibited by salt concentration greater than 100 mM. Uses either magnesium or manganese ions to support helicase activity. Binds strongly to single-stranded DNA in the absence of ATP but dissociates readily in the presence of 1 mM ATP. Binds to RPA1; this interaction promotes HELB recruitment to chromatin following DNA damage (PubMed:12181327, PubMed:22194613, PubMed:26774285). Interacts with at least two subunits of the DNA polymerase alpha complex (PubMed:12181327): Interacts with CDC45 (PubMed:25933514). Interacts with TOPB1 (PubMed:25933514). Predominantly nuclear (PubMed:15146062). Phosphorylation at Ser-967 by CDK2 during the G1/S transition results in its nuclear export into the cytoplasm as cells approach and progress through S phase (PubMed:15146062). Following DNA damage, recruited to sites of double-strand breaks by the RPA complex (PubMed:26774285). Recruited to chromatin following DNA damage induced by UV irradiation, or camptothecin or hydroxyurea treatment (PubMed:22194613). Highly expressed in testis and thymus and weakly in liver, spleen, kidney and brain. Phosphorylated at Ser-967 by CDK2 during the G1/S transition, resulting in its nuclear export into the cytoplasm (PubMed:15146062, PubMed:26774285). As S phase progresses, its exclusion from the nucleus promotes the activation of long-range resection (PubMed:26774285). Belongs to the RecD family. HELB subfamily. Extended N-terminus.