Abstract: We have identified an Aspergillus nidulans gene encoding a RecQ family helicase which we have therefore named recQ. The A. nidulans recQ protein is most closely related in sequence to human recQ helicase 5. Like the latter polypeptide, A. nidulans recQ consists of little more than the conserved helicase domain, lacking the long amino- and carboxy-terminal extensions seen in other recQ family members such as BLM and WRN and in the sole RecQ family helicase of the yeast Saccharomyces cerevisiae (Sgs1p). By analogy with other eukaryotic RecQ helicases, A. nidulans recQ helicase is likely to play an important role in the maintenance of genomic integrity.