ALBERT

Description: Publication date: Available online 13 March 2014 Source: Cell Reports Author(s): Wendan Ren , Hongxia Chen , Qiangzu Sun , Xuhua Tang , Siew Choo Lim , Jun Huang , Haiwei Song The SOSS1 complex comprising SOSSA, SOSSB1, and SOSSC senses single-stranded DNA (ssDNA) and promotes repair of DNA double-strand breaks (DSBs). But how SOSS1 is assembled and recognizes ssDNA remains elusive. The crystal structure of the N-terminal half of SOSSA (SOSSA N ) in complex with SOSSB1 and SOSSC showed that SOSSA N serves as a scaffold to bind both SOSSB1 and SOSSC for assembly of the SOSS1 complex. The structures of SOSSA N /B1 in complex with a 12 nt ssDNA and SOSSA N /B1/C in complex with a 35 nt ssDNA showed that SOSSB1 interacts with both SOSSA N and ssDNA via two distinct surfaces. Recognition of ssDNA with a length of up to nine nucleotides is mediated solely by SOSSB1, whereas neither SOSSC nor SOSSA N are critical for ssDNA binding. These results reveal the structural basis of SOSS1 assembly and provide a framework for further study of the mechanism governing longer ssDNA recognition by the SOSS1 complex during DSB repair. Graphical abstract Teaser The SOSS1 complex senses single-stranded DNA and promotes repair of DNA double-strand breaks (DSBs). Huang, Song, and colleagues have now determined the crystal structures of a truncated form of SOSS1 in isolation and in complex with single-stranded DNA (ssDNA). They show that SOSSA acts as a scaffold for SOSS1 assembly and that SOSSB1 binds to SOSSA and ssDNA through two distinct surfaces. These findings reveal the structural basis of SOSS1 assembly and provide a framework for further elucidating the role of SOSS1 in DSB repair.