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 (Probable). Required for karyogamy during female gametophyte development, when the two polar nuclei fuse to form the diploid central cell nucleus (PubMed:16698901). Component of the FACT complex, a stable heterodimer of SPT16 and SSRP1. Colocalizes with RNA polymerase II on chromatin. Recruited to actively transcribed loci. Widely expressed. Present in embryos, shoots and roots, whereas it is not present in terminally differentiated cells such as mature trichoblasts or cells of the root cap (at protein level). Failure of fusion of the polar nuclei during megagametogenesis. Belongs to the SSRP1 family.