Alternative titles; symbols
HGNC Approved Gene Symbol: SSRP1
Cytogenetic location: 11q12.1 Genomic coordinates (GRCh38) : 11:57,325,988-57,335,892 (from NCBI)
Members of the high mobility group (HMG) protein family (see HMG1, 163905) recognize specific DNA structures. By expression screening of a human B-cell cDNA library, Bruhn et al. (1992) isolated cDNAs encoding a structure-specific recognition protein, SSRP1, that binds specifically to DNA structurally modified by the antitumor drug cisplatin. The SSRP1 cDNA predicts a 709-amino acid protein with a molecular mass of 81,068 Da. The protein has a high percentage (36%) of charged residues grouped into several highly charged domains. SSRP1 has an HMG box located between amino acids 539-614. The SSRP1 protein shows homology to HMG1 and HMG2 (163906) proteins from several species and to a transcription factor, UBF (600673), which also has an HMG-box domain. Northern blot analysis identified a 2.8-kb SSRP1 transcript in all tissues examined. Northern blot analysis of mRNA from testicular and bladder cancer cell lines showed no correlation between SSRP1 mRNA levels and antitumor activity of cisplatin for these tissues. SSRP1 mRNA was not inducible by cisplatin in HeLa cells.
Transcription of naked DNA in eukaryotic cells minimally requires the general transcription factors (see GTF2E1; 189962) and RNA polymerase II (see POLR2A; 180660). This minimal set of factors is not sufficient for transcription by RNA polymerase II in vivo, where DNA is packaged into chromatin by histone octamers (see 142711). One set of accessory factors involved in chromatin remodeling is the SWI/SNF complex (see SMARCC1; 601732). By sequential chromatography, Orphanides et al. (1998) purified FACT (facilitates chromatin remodeling), an accessory factor required for transcript elongation after chromatin remodeling, from HeLa cell nuclear extracts. After the initiation of transcription, FACT acts to release RNA polymerase II from a nucleosome-induced block to allow productive transcription. SDS-PAGE and chromatographic analyses showed that FACT activity is present in an approximately 230-kD protein composed of 140-kD (FACTp140, or SPT16; 605012) and 80-kD (FACTp80) subunits.
By peptide sequence analysis, Orphanides et al. (1999) showed that FACTp80 corresponds to the SSRP1 protein. They proposed that upon transcription activation, FACT is targeted to nucleosomes by the HMG1 domain of SSRP1. When a transcribing RNA polymerase II approaches, FACT promotes disruption of the histone octamer by binding and removing 1 or both histone H2A (see 613499)/H2B (see 609904) dimers.
LeRoy et al. (1998) purified a remodeling and splicing factor, which they termed RSF (see HBXAP; 608522), that is used by polymerases to initiate transcription when DNA is packaged into chromatin. They found that extension of these transcripts requires FACT.
Using a yeast 1-hybrid assay, Spencer et al. (1999) found that human SRF (600589) bound to rat Ssrp1. The interaction was mediated through the MADS box of SRF and amino acids 489 to 542 of Ssrp1, which are immediately adjacent to the HMG domain. Ssrp1 itself did not bind a DNA CArG box, but it did dramatically increase the DNA binding activity of SRF, resulting in synergistic transcriptional activation of native and artificial SRF-dependent promoters. Spencer et al. (1999) concluded that SSRP1 is a coregulator of SRF-dependent transcription in mammalian cells.
Phosphorylation of the human p53 protein (191170) at ser392 is responsive to ultraviolet (UV) but not gamma irradiation. Keller et al. (2001) identified and purified a mammalian UV-activated protein kinase complex that phosphorylates ser392 in vitro. This kinase complex contains casein kinase-2 (CK2; see 115441) and the chromatin transcriptional elongation factor FACT, a heterodimer of SPT16 and SSRP1. In vitro studies showed that FACT alters the specificity of CK2 in the complex such that it selectively phosphorylates p53 over other substrates, including casein. In addition, phosphorylation by the kinase complex was found to enhance p53 activity. These results provided a potential mechanism for p53 activation by UV irradiation.
Saunders et al. (2003) demonstrated that the protein complex FACT is associated with actively transcribed pol II genes on Drosophila polytene chromosomes. FACT displays kinetics of recruitment and of chromosome tracking in vivo similar to pol II and elongation factors Spt5 (602102) and Spt6 (601333). FACT does not colocalize with pol III (see 606007)-transcribed genes, which undergo nucleosome transfer rather than disassembly in vitro. Saunders et al. (2003) concluded that their observations were consistent with FACT being restricted to transcription that involves nucleosome disassembly mechanisms.
Belotserkovskaya et al. (2003) demonstrated that FACT facilitates pol II-driven transcription by destabilizing nucleosomal structure so that 1 histone H2A-H2B dimer is removed during enzyme passage. They also demonstrated that FACT possesses intrinsic histone chaperone activity and can deposit core histones onto DNA. Importantly, FACT activity requires both of its constituent subunits and is dependent on the highly acidic C terminus of its larger subunit, Spt16. Belotserkovskaya et al. (2003) concluded that their findings defined the mechanism by which pol II can transcribe through chromatin without disrupting its epigenetic status.
Cryoelectron Microscopy
Liu et al. (2020) reported 2 cryoelectron microscopy structures of the human histone chaperone FACT, consisting of subunits SPT16 (605012) and SSRP1, in complex with partially assembled subnucleosomes, with supporting biochemical and hydrogen-deuterium exchange data. Liu et al. (2020) found that FACT is engaged in extensive interactions with nucleosomal DNA and all histone variants. The large DNA-binding surface on FACT appears to be protected by the carboxy-terminal domains of both of its subunits, and this inhibition is released by interaction with H2A-H2B, allowing FACT-H2A-H2B to dock onto a complex containing DNA and histones H3 and H4. SPT16 binds nucleosomal DNA and tethers H2A-H2B through its carboxyterminal domain by acting as a placeholder for DNA. SSRP1 also contributes to DNA binding, and can assume 2 conformations, depending on whether a second H2A-H2B dimer is present.
Bruhn et al. (1992) localized the SSRP1 gene to human chromosome 11q12 using a human-rodent hybrid mapping panel.
Belotserkovskaya, R., Oh, S., Bondarenko, V. A., Orphanides, G., Studitsky, V. M., Reinberg, D. FACT facilitates transcription-dependent nucleosome alteration. Science 301: 1090-1093, 2003. [PubMed: 12934006] [Full Text: https://doi.org/10.1126/science.1085703]
Bruhn, S. L., Pil, P. M., Essigmann, J. M., Housman, D. E., Lippard, S. J. Isolation and characterization of human cDNA clones encoding a high mobility group box protein that recognizes structural distortions to DNA caused by binding of the anticancer agent cisplatin. Proc. Nat. Acad. Sci. 89: 2307-2311, 1992. [PubMed: 1372440] [Full Text: https://doi.org/10.1073/pnas.89.6.2307]
Keller, D. M., Zeng, X., Wang, Y., Zhang, Q. H., Kapoor, M., Shu, H., Goodman, R., Lozano, G., Zhao, Y., Lu, H. A DNA damage-induced p53 serine 392 kinase complex contains CK2, hSpt16, and SSRP1. Molec. Cell 7: 283-292, 2001. [PubMed: 11239457] [Full Text: https://doi.org/10.1016/s1097-2765(01)00176-9]
LeRoy, G., Orphanides, G., Lane, W. S., Reinberg, D. Requirement of RSF and FACT for transcription of chromatin templates in vitro. Science 282: 1900-1904, 1998. [PubMed: 9836642] [Full Text: https://doi.org/10.1126/science.282.5395.1900]
Liu, Y., Zhou, K., Zhang, N., Wei, H., Tan, Y. Z., Zhang, Z., Carragher, B., Potter, C. S., D'Arcy, S., Luger, K. FACT caught in the act of manipulating the nucleosome. Nature 577: 426-431, 2020. [PubMed: 31775157] [Full Text: https://doi.org/10.1038/s41586-019-1820-0]
Orphanides, G., LeRoy, G., Chang, C.-H., Luse, D. S., Reinberg, D. FACT, a factor that facilitates transcript elongation through nucleosomes. Cell 92: 105-116, 1998. [PubMed: 9489704] [Full Text: https://doi.org/10.1016/s0092-8674(00)80903-4]
Orphanides, G., Wu, W.-H., Lane, W. S., Hampsey, M., Reinberg, D. The chromatin-specific transcription elongation factor FACT comprises human SPT16 and SSRP1 proteins. Nature 400: 284-288, 1999. [PubMed: 10421373] [Full Text: https://doi.org/10.1038/22350]
Saunders, A., Werner, J., Andrulis, E. D., Nakayama, T., Hirose, S., Reinberg, D., Lis, J. T. Tracking FACT and the RNA polymerase II elongation complex through chromatin in vivo. Science 301: 1094-1096, 2003. [PubMed: 12934007] [Full Text: https://doi.org/10.1126/science.1085712]
Spencer, J. A., Baron, M. H., Olson, E. N. Cooperative transcriptional activation by serum response factor and the high mobility group protein SSRP1. J. Biol. Chem. 274: 15686-15693, 1999. [PubMed: 10336466] [Full Text: https://doi.org/10.1074/jbc.274.22.15686]