The preinitiation complex (PIC) is a multiprotein complex involved in the initiation of transcription, the first step in the process of gene expression. The PIC assembles at the promoter region of a gene before RNA polymerase can initiate transcription. The PIC includes RNA polymerase, the enzyme responsible for synthesizing RNA from a DNA template. In eukaryotes, RNA polymerase II (RNAPII) is responsible for transcribing protein-coding genes. General Transcription Factors (GTFs) are essential proteins that assist RNA polymerase in binding to the promoter and initiating transcription. They include TFIIA, TFIIB, TFIID, TFIIE, TFIIF, and TFIIH. These factors help position RNAPII correctly and facilitate the formation of the PIC. The promoter region of a gene also contains specific DNA sequences that serve as binding sites for GTFs and RNA polymerase. The TATA box, for example, is a common promoter element recognized by TFIID. The process of PIC assembly begins with TFIID binding to the TATA box of the promoter. TFIID is a multi-subunit complex that contains TATA-binding protein (TBP) as its core subunit. TBP recognizes and binds to the TATA box, helping to position the PIC. TFIIB then joins the complex, stabilizing the interaction between TFIID and the promoter DNA. RNA polymerase, along with TFIIF, is recruited next, forming a stable complex with TFIID and TFIIB. TFIIE and TFIIH subsequently join the complex. TFIIH has helicase activity, which is necessary for unwinding the DNA at the transcription start site. Once assembled, the PIC undergoes a series of conformational changes that lead to DNA unwinding at the transcription start site. TFIIH, with its helicase activity, plays a key role in this process. The DNA strands are separated, and a short RNA primer is synthesized by RNA polymerase, typically around 10 to 12 nucleotides in length. After transcription initiation, the GTFs are released from the PIC, although TFIIH remains associated with the elongation complex. The elongation complex therefore includes RNA polymerase, the nascent RNA transcript, and TFIIH. This moves along the DNA template, synthesizing RNA in the 5' to 3' direction. The assembly of the PIC at the promoter is strongly influenced by gene-specific transcriptional activators. These activators bind to enhancer regions, which can be located far from the promoter. Activators and enhancers interact with the PIC through long-range DNA looping, allowing for long-range control of gene expression. Enhancers facilitate the recruitment of the PIC to the promoter, promoting transcription. The formation and activity of the PIC are highly regulated. The rate of transcription initiation can be influenced by factors such as chromatin structure, coactivators, and corepressors. Post-translational modifications of transcription factors and RNA polymerase, such as phosphorylation, can also modulate PIC assembly and function. Additionally, the choice of promoter and the presence of specific regulatory elements in the promoter region contribute to the specificity and regulation of gene transcription. Thus, the preinitiation complex (PIC) is a complex assembly of RNA polymerase, general transcription factors (GTFs), and promoter DNA elements that plays a pivotal role in the initiation of gene transcription. We provide a wide product catalogue of research reagents for investigating the preinitiation complex, including TATA binding protein TBP antibodies, TFII I antibodies, and TFIIB antibodies. Explore our full preinitiation complex product range below and discover more, for less.