title: The Human RecQ helicases, BLM and RECQ1, display distinct DNA substrate specificities.
abstract: RecQ helicases maintain chromosome stability by resolving a number of highly specific DNA structures that would otherwise impede the correct transmission of genetic information. Previous studies have shown that two human RecQ helicases, BLM and WRN, have very similar substrate specificities and preferentially unwind noncanonical DNA structures, such as synthetic Holliday junctions and G-quadruplex DNA. Here, we extend this analysis of BLM to include new substrates and have compared the substrate specificity of BLM with that of another human RecQ helicase, RECQ1. Our findings show that RECQ1 has a distinct substrate specificity compared with BLM. In particular, RECQ1 cannot unwind G-quadruplexes or RNA-DNA hybrid structures, even in the presence of the single-stranded binding protein, human replication protein A, that stimulates its DNA helicase activity. Moreover, RECQ1 cannot substitute for BLM in the regression of a model replication fork and is very inefficient in displacing plasmid D-loops lacking a 3'-tail. Conversely, RECQ1, but not BLM, is able to resolve immobile Holliday junction structures lacking an homologous core, even in the absence of human replication protein A. Mutagenesis studies show that the N-terminal region (residues 1-56) of RECQ1 is necessary both for protein oligomerization and for this Holliday junction disruption activity. These results suggest that the N-terminal domain or the higher order oligomer formation promoted by the N terminus is essential for the ability of RECQ1 to disrupt Holliday junctions. Collectively, our findings highlight several differences between the substrate specificities of RECQ1 and BLM (and by inference WRN) and suggest that these enzymes play nonoverlapping functions in cells.
authors.affiliation: International Centre for Genetic Engineering and Biotechnology Padriciano 99, Trieste, Italy.
authors.forename: Venkateswarlu
authors.initials: V
authors.lastname: Popuri
authors.forename: Csanád Z
authors.initials: CZ
authors.lastname: Bachrati
authors.forename: Laura
authors.initials: L
authors.lastname: Muzzolini
authors.forename: Georgina
authors.initials: G
authors.lastname: Mosedale
authors.forename: Silvia
authors.initials: S
authors.lastname: Costantini
authors.forename: Elisa
authors.initials: E
authors.lastname: Giacomini
authors.forename: Ian D
authors.initials: ID
authors.lastname: Hickson
authors.forename: Alessandro
authors.initials: A
authors.lastname: Vindigni
mesh_terms: D000251:Adenosine Triphosphatases / Q000737:chemistry; D001483:Base Sequence; D004247:DNA / Q000737:chemistry*; D004265:DNA Helicases / Q000737:chemistry*; D054856:G-Quadruplexes; D006801:Humans; D008969:Molecular Sequence Data; D016296:Mutagenesis; D011485:Protein Binding; D011487:Protein Conformation; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D053484:RecQ Helicases / Q000737:chemistry* / Q000502:physiology*; D011994:Recombinant Proteins / Q000737:chemistry; D013379:Substrate Specificity
chemical_list: D011994:Recombinant Proteins; D004247:DNA; D000251:Adenosine Triphosphatases; C097151:Bloom syndrome protein; D004265:DNA Helicases; D053484:RecQ Helicases