SOSS1/2: Sensors of single-stranded DNA at a break

Abstract

In this issue of Molecular Cell, Huang et al. (2009) describe two heterotrimeric single-stranded DNA binding complexes, SOSS1 and SOSS2, that function downstream of the MRN complex to promote DNA repair and the G2/M checkpoint.

Figure 1

The SOSS and RPA single-stranded DNA binding complexes promote double-strand break repair and cell cycle checkpoints. SOSS-A (INTS3), SOSSB1 or SOSSB2 (hSSB1/2), and SOSS-C (C9orf80) form a heterotrimeric ssDNA-binding complex (SOSS) that is recruited to double-strand breaks. SOSS recruitment is dependent on the MRN complex in S/G2 phase cells but is independent of CtIP. In contrast, RPA recruitment depends on both MRN and CtIP, which combine to promote end-resection. The SOSS and RPA complexes are both targets and regulators of the ATM and ATR checkpoint kinases.