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. Transcription elongation is promoted by the repression of transcription initiation from cryptic sites. Also acts in establishing transcription initiation complexes and promotes SPT15/TBP-binding to a TATA box. Together with replication factor-A protein (RPA), FACT may play a role in nucleosome deposition during DNA replication. Forms a stable heterodimer with POB3 (PubMed:9832518, PubMed:9705338, PubMed:10413469). The SPT16-POB3 dimer weakly associates with multiple molecules of NHP6 (NHP6A or NHP6B) to form the FACT (yFACT or SNP) complex (PubMed:11432837, PubMed:11313475, PubMed:12952948). The FACT complex interacts with the CK2 (casein kinase II) complex subunits CKA1, CKA2, CKB1 and CKB2 and the components of the transcription machinery CHD1, CTR9, PAF1 and CDC73 (PubMed:12682017, PubMed:12242279). The FACT complex interacts with the PAF1 complex (PubMed:11927560). Interacts with POL1 (PubMed:9199353). Interacts with SAS3 (PubMed:10817755). Interacts with YTA7 (PubMed:22156209). Colocalizes with RNA polymerase II on chromatin (PubMed:10413469, PubMed:14585989, PubMed:14739930). Recruited to actively transcribed loci (PubMed:14585989). Associates with the coding region of HTA1 (PubMed:19683497). Present with 18500 molecules/cell in log phase SD medium. Belongs to the peptidase M24 family. SPT16 subfamily. Although related to the peptidase M24 family, this protein lacks conserved active site residues suggesting that it may lack peptidase activity.