3'-5' DNA helicase of conserved RecQ family; involved in interstrand crosslink repair, nucleotide-excision repair, telomerase-independent telomere maintenance; binds telomeres, modulates telomerase activity with Pif1p, inhibits telomere addition to dsDNA breaks; lacks ssDNA annealing and strand exchange activities; N-terminal domain has DNA-binding site needed for repair of DNA inter-strand crosslinks; human homolog RecQL4 is involved in Rothmund-Thomson, Baller-Gerold and RAPADILINO syndromes