selective factor 1

SL1 was discovered by Robert Tjian and his colleagues in 1985 when they separated a HeLa cell extract into two functional fractions.{{cite journal | vauthors = Hochheimer A, Tjian R | title = Diversified transcription initiation complexes expand promoter selectivity and tissue-specific gene expression | journal = Genes & Development | volume = 17 | issue = 11 | pages = 1309–20 | year = 2003 | pmid = 12782648 | doi = 10.1101/gad.1099903 | doi-access = free }} One factor has RNA polymerase I activity, but no ability to initiate accurate transcription of a human rRNA template. This transcription factor, SL1, showed species specificity.{{cite journal | vauthors = Hempel WM, Cavanaugh AH, Hannan RD, Taylor L, Rothblum LI | title = The species-specific RNA polymerase I transcription factor SL-1 binds to upstream binding factor | journal = Molecular and Cellular Biology | volume = 16 | issue = 2 | pages = 557–63 | year = 1996 | pmid = 8552083 | pmc = 231034 | doi = 10.1128/MCB.16.2.557 }} That is, it could distinguish between the human and mouse rRNA promoter,{{cite book | url = {{google books |plainurl=yes |id=jnTEbintTj0C | page=110 }} |title=The Nucleolus |publisher= |date=2011-09-15 |accessdate=2014-08-10}} and added increasing amount of human template at the expense of the mice template.{{cite journal | vauthors = Learned RM, Cordes S, Tjian R | title = Purification and characterization of a transcription factor that confers promoter specificity to human RNA polymerase I | journal = Molecular and Cellular Biology | volume = 5 | issue = 6 | pages = 1358–69 | year = 1985 | pmid = 3929071 | pmc = 366865 | doi = 10.1128/MCB.5.6.1358 }} Tijian and coworkers went on to show that by footprinting a partially purified polymerase 1 preparation could bind to the human rRNA promoter. In particular it causes a footprint over a region of the UCE called A site.{{cite web| url=https://patents.google.com/patent/US5637686 |title=Patent US5637686 - Tata-binding protein associated factor, nucleic acids - Google Patents |date= |access-date=2014-08-10}} This binding is not due to polymerase I itself but to a transcription factor called upstream binding factor, UBF.

SLI functions in assembling the transcription preinitiation complex. It is also a major determinant of species-specificity in ribosomal RNA gene transcription. Research suggests that UBF and SL1 act synergistically to stimulate transcription. Recent investigation also suggests that SL1 is a target for cancer therapy.{{cite journal | vauthors = Villicaña C, Cruz G, Zurita M | title = The basal transcription machinery as a target for cancer therapy | journal = Cancer Cell International | volume = 14 | issue = 1 | pages = 18 | year = 2014 | pmid = 24576043 | pmc = 3942515 | doi = 10.1186/1475-2867-14-18 | doi-access = free }}

SL1 is composed of the TATA-binding protein and at least four TAF (TATA box-binding protein-associated factor) subunits (TAF1A, TAF1B,TAF1C and TAF1D).{{cite journal | vauthors = Friedrich JK, Panov KI, Cabart P, Russell J, Zomerdijk JC | title = TBP-TAF complex SL1 directs RNA polymerase I pre-initiation complex formation and stabilizes upstream binding factor at the rDNA promoter | journal = The Journal of Biological Chemistry | volume = 280 | issue = 33 | pages = 29551–8 | year = 2005 | pmid = 15970593 | pmc = 3858828 | doi = 10.1074/jbc.M501595200 | doi-access = free }} It is therefore possible to inhibit SL1 activity with anti-TBP antibodies.

• RNA polymerase I
• RNA polymerase III
• Transcription preinitiation complex

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Category:Transcription factors