FACT (facilitates chromatin transcription,[1] sometimes facilitates chromatin transactions[2][3]) is a heterodimeric protein complex that affects eukaryotic RNA polymerase II (Pol II) transcription elongation both in vitro and in vivo.
It was discovered in 1998 as a factor purified from human cells that was essential for productive, in vitro Pol II transcription on a chromatinized DNA template.
Deletion of the highly acidic C-terminus of Spt16 (a common feature of known histone chaperones) does not prevent Spt16 from forming a stable complex with SSRP1, but it does eliminate interaction with mononucleosomes and ability to stimulate in vitro transcription on chromatinized templates.
These two subunits are highly conserved across all eukaryotes, and in addition to transcription, have been shown to affect DNA repair and replication as well.
[6] In cells, FACT is enriched on parts of the genome involved in actively elongating Pol II, as seen in fluorescent-antibody staining of Drosophila polytene chromosomes and chromatin immunoprecipitation (ChIP) assays on Drosophila Kc cell extracts.