Selective factor 1 explained

Selective factor 1 (also known as SL1) is a transcription factor that binds to the promoter of genes and recruits a preinitiation complex to which RNA polymerase I will bind to and begin the transcription of ribosomal RNA (rRNA).^{[1] [2]}

Discovery

SL1 was discovered by Robert Tjian and his colleagues in 1985 when they separated a HeLa cell extract into two functional fractions.^[3] 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.^[4] That is, it could distinguish between the human and mouse rRNA promoter,^[5] and added increasing amount of human template at the expense of the mice template.^[6] 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.^[7] This binding is not due to polymerase I itself but to a transcription factor called upstream binding factor, UBF.

Function

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.^[8]

Structure

SL1 is composed of the TATA-binding protein and three TAF (TATA box-binding protein-associated factor) subunits (TAF1A, TAF1B, and TAF1C).^[9] It is therefore possible to inhibit SL1 activity with anti-TBP antibodies.

See also

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

Notes and References

1. Tuan JC, Zhai W, Comai L . Recruitment of TATA-binding protein-TAFI complex SL1 to the human ribosomal DNA promoter is mediated by the carboxy-terminal activation domain of upstream binding factor (UBF) and is regulated by UBF phosphorylation . Molecular and Cellular Biology . 19 . 4 . 2872–9 . 1999 . 10082553 . 84080 . 10.1128/MCB.19.4.2872 .
2. Book: [{{Google books | plainurl=yes | id = yXFfPkLq4yEC | page = 555 }} Lewin's Genes XI ]. 2014-08-10.
3. Hochheimer A, Tjian R . Diversified transcription initiation complexes expand promoter selectivity and tissue-specific gene expression . Genes & Development . 17 . 11 . 1309–20 . 2003 . 12782648 . 10.1101/gad.1099903 . free .
4. Hempel WM, Cavanaugh AH, Hannan RD, Taylor L, Rothblum LI . The species-specific RNA polymerase I transcription factor SL-1 binds to upstream binding factor . Molecular and Cellular Biology . 16 . 2 . 557–63 . 1996 . 8552083 . 231034 . 10.1128/MCB.16.2.557 .
5. Book: [{{google books |plainurl=yes |id=jnTEbintTj0C | page=110 }} The Nucleolus ]. 2011-09-15 . 2014-08-10.
6. Learned RM, Cordes S, Tjian R . Purification and characterization of a transcription factor that confers promoter specificity to human RNA polymerase I . Molecular and Cellular Biology . 5 . 6 . 1358–69 . 1985 . 3929071 . 366865 . 10.1128/MCB.5.6.1358 .
7. Web site: Patent US5637686 - Tata-binding protein associated factor, nucleic acids - Google Patents . 2014-08-10.
8. Villicaña C, Cruz G, Zurita M . The basal transcription machinery as a target for cancer therapy . Cancer Cell International . 14 . 1 . 18 . 2014 . 24576043 . 3942515 . 10.1186/1475-2867-14-18 . free .
9. Friedrich JK, Panov KI, Cabart P, Russell J, Zomerdijk JC . TBP-TAF complex SL1 directs RNA polymerase I pre-initiation complex formation and stabilizes upstream binding factor at the rDNA promoter . The Journal of Biological Chemistry . 280 . 33 . 29551–8 . 2005 . 15970593 . 3858828 . 10.1074/jbc.M501595200 . free .