Component of the FACT complex, a general chromatin factor that acts to reorganize nucleosomes. The FACT complex is involved in multiple processes that require DNA as a template such as mRNA elongation, DNA replication and DNA repair. During transcription elongation the FACT complex acts as a histone chaperone that both destabilizes and restores nucleosomal structure. It facilitates the passage of RNA polymerase II and transcription by promoting the dissociation of one histone H2A-H2B dimer from the nucleosome, then subsequently promotes the reestablishment of the nucleosome following the passage of RNA polymerase II. Binds specifically to double-stranded DNA (By similarity). Component of the FACT complex, a stable heterodimer of SSRP1 and SUPT16H. May also be a component of a CK2-SPT16-SSRP1 complex, composed of SSRP1, SUPT16H, CSNK2A1, CSNK2A2 and CSNK2B (By similarity). Colocalizes with RNA polymerase II on chromatin. Recruited to actively transcribed loci. Belongs to the SSRP1 family.