DNA-binding properties of Smc6, a core component of the Smc5–6 DNA repair complex

The Smc5–6 complex is an essential regulator of chromosome integrity and a key component of the DNA damage response. As an essential DNA repair factor, the Smc5–6 complex is expected to interact with DNA and/or chromatin during the execution of its functions. How the Smc6 protein promotes the binding of the Smc5–6 complex to DNA lesions is currently unknown. We show here that Smc6 is a strong DNA-binding protein with a clear preference for single-stranded DNA substrates. Importantly, Smc6 associates with DNA in the absence of other Smc5–6 complex components and its activity is modulated by nucleotides. Our results also show that the minimal size of single-stranded DNA required for tight association with Smc6 is ∼60 nucleotides in length. Taken together, our results suggest that Smc6 contributes to DNA repair in vivo by targeting the Smc5–6 complex to single-stranded DNA substrates created during the processes of homologous recombination and/or DNA replication.

► We report the first biochemical characterization of purified full-length Smc6.
► Smc6 is an ATP-regulated and conformation-sensitive DNA-binding protein.
► Smc6 has a clear preference for binding to single-stranded DNA substrates.
► Our results implicate Smc6 as a major DNA-targeting component of the Smc5–6 complex.