FACT (facilitates chromatin transcription,[1] sometimes facilitates chromatin transactions[2][3]) is a
heterodimericprotein complex that affects
eukaryoticRNA 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.[4]
FACT consists of 140 and 80
kilodalton (kDa) subunits. The 140 kDa subunit is encoded by the human gene
SUPT16H, (SPT16 in S. cerevisiae) while the 80 kDa subunit is encoded by the human gene
SSRP1 (POB3 in S. cerevisiae). Both of these subunits in yeast affect Pol II transcription elongation, and purified human FACT binds specifically to mononucleosomes and the histone
H2A/
H2B dimer, but not to the
H3/
H4 tetramer (see:
Nucleosome core particle) or Pol II.[5]
Co-immunoprecipitation assays with tagged
recombinant proteins showed that the Spt16 subunit interacts with H2A/H2B dimers and mononucleosomes, but not H3/H4 tetramers, whereas the SSRP1 subunit interacts only with H3/H4 tetramers and not mononucleosomes. 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. The two subunits together, but neither alone, can stimulate formation of nucleosomes from free histones and DNA (histone
chaperone activity). 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]
^Saunders, Abbie; Werner, Janis; Andrulis, Erik D.; Nakayama, Takahiro; Hirose, Susumu; Reinberg, Danny; Lis, John T. (2003). "Tracking FACT and the RNA Polymerase II Elongation Complex Through Chromatin in Vivo". Science. 301 (5636): 1094–1096.
Bibcode:
2003Sci...301.1094S.
doi:
10.1126/science.1085712.
PMID12934007.
S2CID10064786.
Further reading
Reinberg, D., Sims, R. (2006).
de FACTo nucleosome dynamics. Journal of Biological Chemistry, 281(33) 23297-23391.