RNA polymerase II and general transcription factors (GTFs) assemble on a promoter to form a transcription preinitiation complex (PIC). Among the GTFs, TFIIE recruits TFIIH to complete the PIC formation and regulates enzymatic activities of TFIIH. However, the mode of binding between TFIIE and TFIIH is poorly understood. Here, we demonstrate the specific binding of the C-terminal acidic domain (AC-D) of the human TFIIEa subunit to the pleckstrin homology domain (PH-D) of the human TFIIH p62 subunit and describe the solution structures of the free and PH-D-bound forms of AC-D. Although the flexible N-terminal acidic tail from AC-D wraps around PH-D, the core domain of AC-D also interacts with PH-D. AC-D employs an entirely novel binding mode, which differs from the amphipathic helix method used by many transcriptional activators. So the binding surface between PH-D and AC-D is much broader than the specific binding surface between PH-D and the p53 acidic fragments. From our in vitro studies, we demonstrate that this interaction could be a switch to replace p53 with TFIIE on TFIIH in transcription.

Nucleotide excision repair is initiated by two different damage recognition subpathways, global genome repair (GGR) and transcription-coupled repair (TCR). In GGR, XPC detects DNA lesions and recruits TFIIH via interaction with the pleckstrin homology (PH) domain of TFIIH subunit p62. In TCR, an elongating form of RNA Polymerase II detects a lesion on the transcribed strand and recruits TFIIH by an unknown mechanism. Here, we found that the TCR initiation factor UVSSA forms a stable complex with the PH domain of p62 via a short acidic string in the central region of UVSSA, and determined the complex structure by NMR. The acidic string of UVSSA binds strongly to the basic groove of the PH domain by inserting Phe408 and Val411 into two pockets, highly resembling the interaction mechanism of XPC with p62. Mutational binding analysis validated the structure and identified residues crucial for binding. TCR activity was markedly diminished in UVSSA-deficient cells expressing UVSSA mutated at Phe408 or Val411. Thus, a common TFIIH recruitment mechanism is shared by UVSSA in TCR and XPC in GGR.

The transactivation domain (TAD) of tumor suppressor p53 has homologous subdomains, TAD1 and TAD2. Both are intrinsically disordered in their free states, but all structures of TAD1 and TAD2 bound to their target proteins have demonstrated use of an amphipathic α-helix, suggesting that the binding-coupled helix folding mechanism of TAD1 and TAD2 is essential. Although phosphorylation of TAD is important to switch the function of p53, bound structures of phosphorylated TAD1 and TAD2 have not been determined. Here, we reveal the recognition mechanism of the phosphorylated TAD2 bound to a pleckstrin homology (PH) domain from human TFIIH subunit p62 in an extended string-like conformation. This string-like binding mode of TAD2 seems to be independent of its phosphorylation in spite of enhanced binding activity upon phosphorylation. This is in contrast to the amphipathic helical binding mode of the unphosphorylated TAD2 to the yeast tfb1 PH domain and demonstrates that the p53 TAD2 has much higher conformational malleability than previously appreciated.

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