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). In embryos, may function redundantly with hmg-3 in embryos to promote cell cycle progression and development of the anterior pharynx (PubMed:30336114). In the germline, acts non-redundantly with hmg-3 to play a role in oocyte development (PubMed:30336114). Component of the FACT complex, a stable heterodimer of hmg-4 and spt-16 (Probable). The FACT complex may also include hmg-3 instead of hmg-4 (Probable). Expressed in the germline and somatic cells. Expressed throughout development (PubMed:30336114). First expressed in embryos at the 1-cell stage (PubMed:30336114). RNAi-mediated knockdown at the L4 larval stage results in less than 10% embryonic lethality in offspring or death at the larval stage (PubMed:30336114). RNAi-mediated knockdown at the L1 larval stage results in sterile animals, which do not seem to produce mature oocytes, but that survive to adulthood (PubMed:30336114). Double RNAi-mediated knockdown at the L4 larval stage with hmg-3 results in 60% embryonic lethality in offsping (PubMed:30336114). Double RNAi-mediated knockdown with hmg-3 in embryos results in defective cell cycle initiation, duration and completion and in failed development of the anterior pharynx (PubMed:30336114). Belongs to the SSRP1 family.