TFIIIB

SANT SW13, ADA2, N-CoR and TFIIIB, DNA-binding domains E(MFP)B 18(31) 18(31) 1A5J... 

Bachman N, Gelbart ME, Tsukiyama T, Boeke JD (2005) TFIIIB subunit Bdplp is required for periodic integration of the Tyl retrotransposon and targeting of isw2p to S. cerevisiae tDNAs. Genes Dev 19 955-964... 

TFIIIC subunits TFIIIC90 and TFIIICllO. The known function of TFIIIC is to initiate transcription complex formation by binding to promoter DNA and recruiting TBP-containing TFIIIB and RNA polymerase III, that directs synthesis of tRNA precursors. TFIIIC have an intrinsic HAT activity. 

Fig. 13.11. Substrates and phase-spedfic activation of CDKs in the ceU cycle. An overview is shown of the phase-specific activation of the most important CDK-cychn complexes and of selected substrates. The arrows indicate activation and phosphorylation. CDK cycMn-dependent protein kinase p53 tumor suppressor p53 pRb tumor suppressor pRb CDC25 CDC25 phosphatase TFIIIB transcription factor TFIIIB R restriction point.

Examples of proteins that are specifically phosphorylated during the cell cycle are the lamins. Hyperphosphorylation of the lamins leads to disintegration of the nuclear lamina. Myosin in actin-myosin filaments is also specifically phosphorylated during mitosis. Other M-phase-specific phosphorylations occur at transcription factor TFIIIB, leading to inhibition of transcription by RNA polymerase III. Phosphorylation of TAP proteins (see 1.4.2.3) is also involved in general inhibition of banscription. 

After TFIIIA binds, proteins TFIIIC and then TFII-IB also bind. Although promoters of classes 2 and 3 do not require TFIIIA, all three classes depend upon TFIIIB and TFIIIC.484 The TATA-binding protein TBF is one of three components present in TFIIIB, which may be regarded as the true initiation factor.47 485 Both TFIIIA and TFIIIC can be described as assembly factors 47 A silkworm RNA pol III has been reported to require a transcription factor consisting of RNA 486... 

Eukaryotic cells contain multiple copies of the 5S rRNA gene. Unlike other eukaryotic rRNA genes, the 5S rRNA genes are transcribed by RNA Pol III. Two control elements, an A box and a C box, lie downstream of the transcriptional start site. The C box binds TFIIIA which then recruits TFIIIC. TFIIIB now binds and interacts with RNA Pol III to form the transcription initiation complex. Transcription produces a mature 5S rRNA that requires no processing. 

In eukaryotes, the tRNA genes exist as multiple copies and are transcribed by RNA polymerase III (RNA Pol III). As in prokaryotes, several tRNAs may be transcribed together to yield a single pre-tRNA molecule that is then processed to release the mature tRNAs. The promoters of eukaryotic tRNA genes are unusual in that the transcriptional control elements are located downstream (i.e. on the 3 side) of the transcriptional start site (at position +1). In fact they lie within the gene itself. Two such elements have been identified, called the A box and B box (Fig. 3). Transcription of the tRNA genes by RNA Pol III requires transcription factor IIIC (TFIIIC) as well as TFIIIB. THIIC binds to the A and B boxes whilst TFIIIB binds upstream of the A box. TFIIIB contains three subunits, one of which is TBP (TATA binding protein), the polypeptide required by all three eukaryotic RNA polymerases. 

Three general transcription factors are required for Pol III to Initiate transcription of tRNA and SS-rRNA genes In vitro. Two multimeric factors, TFIIIC and TFIIIB, participate In Initiation at both tRNA and SS-rRNA promoters a third factor, TFIIIA, Is required for initiation at SS-rRNA promoters. As with assembly of Pol I and Pol II Initiation complexes, the Pol III general transcription factors bind to promoter DNA in a defined sequence. 

The N-terminal half of one TFIIIB subunit, called BRF (for TFIIB-related factor), is similar In sequence to TFIIB (a Pol II factor). This similarity suggests that BRF and TFIIB perform a similar function in initiation, namely, to direct the polymerase to the correct start site. Once TFIIIB has bound to either a tRNA or SS-rRNA gene, Pol III can bind and Initiate transcription In the presence of ribonucleoside triphosphates. The BRF subunit of TFIIIB interacts specifically with one of the polymerase subunits unique to Pol III, accounting for Initiation by this specific nuclear RNA polymerase. 

Another of the three subunits composing TFIIIB is TBP, which we can now see Is a component of a general transcription factor for all three eukaryotic nuclear RNA polymerases. The finding that TBP participates In transcription Initiation by Pol I and Pol III was surprising, since the promoters recognized by these enzymes often do not contain TATA boxes. Nonetheless, recent studies Indicate that the TBP subunit of TFIIIB Interacts with DNA similarly to the way It Interacts with TATA boxes. 

S Ribosomal RNA genes - The most thoroughly studied genes transcribed by RNA polymerase III are those for 5S ribosomal RNA. At least three protein factors in addition to polymerase III are needed for the expression of the 5S rRNA genes in vitro. Two of these transcription factors (TFIIIB and TFIIIC) appear to participate in the transcription of tRNA genes as well, but one (called TFIIIA) is specific for the 5S genes. 

TETRATRICOPEPTIDE REPEATS OF TFC4 AND A LIMITING STEP IN THE ASSEMBLY OF THE INITIATION FACTOR TFIIIB... 

VI. Ordered Binding of TFIIIB Subunits to TFIIIC-DNA and Dynamic... 

This chapter focuses on recent advances in our understanding of a critical limiting step in Pol III transcription the assembly on DNA of the initiation factor TFIIIB by TFIIIC. 

In contrast to its minor role in TATA-directed assembly of TFIIIB, the TBlIB-like region of Brfl plays a major role in Pol III recruitment and promoter melting (Hahn and Roberts, 2000 Kassavetis et al., 1998, 2001). The TFIIB-core region of Brfl is sufficient for a binary interaction with two Pol Ill-specific subunits, Rpcl7 and Rpc34 (Ferri et al., 2000 Khoo et al.,... 

Tfc4 Fragment Global Kjj TFIIIB Inhibition nM SEa nH Hill Coefficient... 

Tfc4 Fragment Global Kd TFIIIB inhibition (nM SE°) Global KdTFIIIB inhibition (nM SE°) Global Kd TFIIIB inhibition (nm SEa)... 

Tfc4 also interacts directly with the Bdpl subunit of TFIIIB (Dumay-Odelot et al., 2002 Ruth et al., 1996), and this interaction, like that for Brfl, involves both TPR arrays (Ishiguro et al., 2002 Liao et al., 2003 ... 

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