SOSS complexes participate in the maintenance of genomic stability.

Proteins that bind to single-stranded DNA (ssDNA) are essential for DNA replication, recombinational repair, and maintenance of genomic stability. Here, we describe the characterization of an ssDNA-binding heterotrimeric complex, SOSS (sensor of ssDNA) in human, which consists of human SSB homologs hSSB1/2 (SOSS-B1/2) and INTS3 (SOSS-A) and a previously uncharacterized protein C9orf80 (SOSS-C). We have shown that SOSS-A serves as a central adaptor required not only for SOSS complex assembly and stability, but also for facilitating the accumulation of SOSS complex to DNA ends. Moreover, SOSS-depleted cells display increased ionizing radiation sensitivity, defective G2/M checkpoint, and impaired homologous recombination repair. Thus, our study defines a pathway involving the sensing of ssDNA by SOSS complex and suggests that this SOSS complex is likely involved in the maintenance of genome stability.