RECQL5 has unique strand annealing properties relative to the other human RecQ helicase proteins

• The RecQ helicases all have strand annealing activities, very important in genome maintenance.
• We have compared the helicase and strand annealing properties of all 5 human RecQ helicases.
• RECQ5 has unique annealing properties including RNA:DNA annealing.

The RecQ helicases play important roles in genome maintenance and DNA metabolism (replication, recombination, repair, and transcription). Five different homologs are present in humans, three of which are implicated in accelerated aging genetic disorders: Rothmund Thomson (RECQL4), Werner (WRN), and Bloom (BLM) syndromes. While the DNA helicase activities of the 5 human RecQ helicases have been extensively characterized, much less is known about their DNA double strand annealing activities. Strand annealing is an important integral enzymatic activity in DNA metabolism, including DNA repair. Here, we have characterized the strand annealing activities of all five human RecQ helicase proteins and compared them. Interestingly, the relative strand annealing activities of the five RecQ proteins are not directly (inversely) related to their helicase activities. RECQL5 possesses relatively strong annealing activity on long or small duplexed substrates compared to the other RecQs. Additionally, the strand annealing activity of RECQL5 is not inhibited by the presence of ATP, unlike the other RecQs. We also show that RECQL5 efficiently catalyzes annealing of RNA to DNA in vitro in the presence or absence of ATP, revealing a possible new function for RECQL5. Additionally, we investigate how different known RecQ interacting proteins, RPA, Ku, FEN1 and RAD51, regulate their strand annealing activity. Collectively, we find that the human RecQ proteins possess differential DNA double strand annealing activities and we speculate on their individual roles in DNA repair. This insight is important in view of the many cellular DNA metabolic actions of the RecQ proteins and elucidates their unique functions in the cell.

A model of RecQ helicases function to strand unwinding or strand annealing. A model of RecQ helicases function to strand unwinding or strand annealing. (a) () represent weak helicase activity (RECQL5 and RECQL4) and (⟵) represent strong helicase activity (WRN, BLM and RECQL1). () represent strong strand annealing activity (RECQL5) in the presence or absence of ATP and () represent inhibition of strand annealing activity (RECQL1, RECQL1, WRN and BLM) in the presence of ATP (see Table 2). (b) RECQL5 promotes annealing of RNA to dsDNA in the presence or absence of ATP whereas remaining four RecQ helicases could not anneal RNA to dsDNA (±ATP). () represent RecQ helicase.Figure optionsDownload high-quality image (62 K)Download as PowerPoint slideFigure optionsDownload high-quality image (57 K)Download as PowerPoint slideFigure optionsDownload high-quality image (40 K)Download as PowerPoint slideFigure optionsDownload high-quality image (33 K)Download as PowerPoint slideFigure optionsDownload high-quality image (81 K)Download as PowerPoint slide