Enables 5'-flap endonuclease activity. Involved in mitotic telomere maintenance via semi-conservative replication and nucleic acid phosphodiester bond hydrolysis. Located in chromosome, telomeric region. Human ortholog(s) of this gene implicated in Seckel syndrome 8; autosomal dominant progressive external ophthalmoplegia with mitochondrial DNA deletions 6; isolated growth hormone deficiency type IA; and mitochondrial myopathy. Orthologous to human DNA2 (DNA replication helicase/nuclease 2). [provided by Alliance of Genome Resources, Apr 2022]