Transcription carboxyl-terminal domain

Another important coactivator consists of 20 or more polypeptides in a protein complex called mediator (Fig. 28-27) the 20 core polypeptides are highly conserved from fungi to humans. Mediator binds tightly to the carboxyl-terminal domain (CTD) of the largest subunit of Pol II. The mediator complex is required for both basal and regulated transcription at promoters used by Pol II, and it also stimulates the phosphorylation of the CTD by TFIIH. Both mediator and TFIID are required at some promoters. As with TFIID, some DNA-binding transactivators interact with one or more components of the mediator complex. Coactivator complexes function at or near the promoter s TATA box. 

TBP bound to the TATA box is the heart of the initiation complex (see Figure 28.19). The surface of the TBP saddle provides docking sites for the binding of other components (Figure 28.21). Additional transcription factors assemble on this nucleus in a defined sequence. TFIIA is recruited, followed by TFIIB and then TFIIF—an ATP-dependent helicase that initially separates the DNA duplex for the polymerase. Finally, RNA polymerase II and then TFIIE join the other factors to form a complex called the basal transcription apparatus. Sometime in the formation of this complex, the carboxyl-terminal domain of the polymerase is phosphorylated on the serine and threonine residues, a process required for successful initiation. The importance of the carboxyl-terminal domain is highlighted by the finding that yeast containing mutant polymerase II with fewer than 10 repeats is not viable. Most of the factors are released before the polymerase leaves the promoter and can then participate in another round of initiation. 

Eukaryotic cells have three types of RNA polymerases. Binding of RNA polymerase II to its promoters requires an array of proteins called transcription factors. Elongation factors participate in the elongation phase of transcription. The largest subunit of Pol II has a long carboxyl-terminal domain, which is phosphorylated during the initiation and elongation phases. 

The a subunit, the gene product (329 amino acids, 36,512) of rpoA, is required for the assembly of the core enzyme and plays a role in promoter recognition. When phage T4 infects E. coli, an Arg residue of the a subunit is modified by ADP-ribosylation which results in a reduction of the affinity of the promoter to the holoenzyme. The carboxyl-terminal domain (CTD, 99 amino acids) is regarded as the contact site for transcription activators, e.g.. 

HSF3, identified in chicken, is induced by c-Myb in the absence of cellular stress (Nakai and Morimoto, 1993 Kanei-Ishii et al., 1997). Another isoform of HSF found in human cells, HSF4, possesses transcription represser properties in vivo (Frejtag et al., 2001). Comparisons of HSF protein structure in these organisms indicate the presence of conserved DNA binding domain and three hydrophobic heptad repeats that constitute the trimerization domain. These domains are located within the amino-terminal region of the protein. The stress-responsive transcriptional activation domain is located in the carboxyl-terminal region of the molecule. 

The downstream effectors of TRAF signaling are transcription factors in the nuclear factor k-B (NF-kB) and activator protein-1 (AP-1) family (Ghosh and Karin, 2002 Shaulian and Karin, 2002), which can turn on numerous genes involved in many aspects of cellular and immune functions. While the carboxyl terminal TRAF domain, containing a coiled-coil TRAF-N domain and a conserved TRAF-C domain, is both necessary and sufficient for TRAF self-association and receptor interaction, the amino terminal domain, containing RING and zinc-finger motifs, is important for downstream functions (Rothe et al, 1994). 

Song L-N, Huse B, Rusconi S, Simons SS Jr. Transactivation specificity of glucocorticoi vs. progesterone receptors Role of 106. functionally different interactions of transcription factors with amino- and carboxyl-terminal receptor domains. J. Biol. Chem. 2001 276 24806-24816 Szapary D, Song L-N, He Y, Simons 107. SS, Jr. Comparison of modulatory actions of GME, GMEB-2,... 

Skinner, M., S. Qu, C. Moore and R. Wisdom. Transcriptional activation and transformation by FosB protein require phosphorylation of the carboxyl-terminal activation domain. Mol. Cell. Biol. 17 2372-2380, 1997. 

In two-component systems in bacteria (Fig. 4), signal perception by the A -terminal domain of the sensor (which is usually located in the periplasmic space flanked by two or more transmembrane domains) results in autophosphorylation of a carboxyl-terminal histidine kinase domain, the phosphate group is then transferred to an aspartate residue in the A -terminal of the receiver domain of the response regulator which in turn via the output domain regulates its activity - for example as a transcriptional activator [42]. 

The identification of the cis-acting sequences and protein factors involved in ribosomal DNA transcription strongly suggested that the network of protein-protein and protein—DNA interactions among UBF, SL1, and the promoter elements plays a major role in the assembly of a stable preinitiation complex. A number of studies have established that UBF and SL1 play a key role in this process and are necessary to direct a high level of RNA Pol I transcription in vitro. The current stepwise model of factors assembly predicts that the binding of UBF dimer to the UCE and CORE elements is a prerequisite for the recruitment of the selectivity factor SL1 to the rDNA promoter (Fig. 4, step I). Biochemical studies have indicated that two subunits of SL1, TAFi-18 and TBP, interact directly with the carboxy-terminal acidic domain of UBF (Beckmann et al., 1995 Tuan et al., 1999 step II). This finding demonstrates that the function of the carboxyl-terminal activation domain of UBF is to recruit the essential... 

---