pointed out that the homology of the WRN protein to members of the RecQ family of DNA helicases does not necessarily mean that the WRN gene encodes an active helicase. For example, the Saccharomyces cerevisiae RAD26 gene protein and the human transcription-repair coupling factor mutant in Cockayne syndrome B (609413) are highly homologous to known helicases, yet neither encodes an active helicase. Gray et al. (1997) reported work indicating that the Werner syndrome protein does indeed catalyze DNA unwinding.