Component of the SOSS complex, a multiprotein complex that functions downstream of the MRN complex to promote DNA repair and G2/M checkpoint. In the SOSS complex, acts as a sensor of single-stranded DNA that binds to single-stranded DNA. The SOSS complex associates with DNA lesions and influences diverse endpoints in the cellular DNA damage response including cell-cycle checkpoint activation, recombinational repair and maintenance of genomic stability. Required for efficient homologous recombination-dependent repair of double-strand breaks (DSBs) (By similarity). Component of the SOSS complex, composed of soss-b (soss-b1/nabp2 or soss-b2/nabp1), soss-a/ints3 and soss-c/inip. SOSS complexes containing soss-b1/nabp2 are more abundant than complexes containing soss-b2/nabp1 (By similarity). Localizes to nuclear foci following DNA damage. Belongs to the SOSS-B family. SOSS-B1 subfamily.