<P> General transcription factors are a group of proteins involved in transcription initiation and regulation . These factors typically have DNA - binding domains that bind specific sequence elements of the core promoter and help recruit RNA polymerase to the transcriptional start site . General transcription factors for RNA polymerase II include TFIID, TFIIA, TFIIB, TFIIF, TFIIE, and TFIIH . </P> <P> To prepare for transcription, a complete set of general transcription factors and RNA polymerase need to be assembled at the core promoter to form the ~ 2 million dalton preinitiation complex . For example, for promoters that contain a TATA box near the TSS, the recognition of TATA box by the TBP subunit of TFIID initiates the assembly of a transcription complex . The next proteins to enter are TFIIA and TFIIB, which stabilize the DNA - TFIID complex and recruit Pol II in association with TFIIF and additional transcription factors . TFIIF serves as the bridge between the TATA - bound TBP and polymerase . One of the last transcription factors to be recruited to the preinitiation complex is TFIIH, which plays an important role in promoter melting and escape . </P> <P> For pol II - transcribed genes, and unlike bacterial RNA polymerase, promoter melting requires hydrolysis of ATP and is mediated by TFIIH . TFIIH is a ten - subunit protein, including both ATPase and protein kinase activities . While the upstream promoter DNA is held in a fixed position by TFIID, TFIIH pulls downstream double - stranded DNA into the cleft of the polymerase, driving the separation of DNA strands and the transition of the preinitiation complex from the closed to open state . TFIIB aids in open complex formation by binding the melted DNA and stabilizing the transcription bubble . </P> <P> Once the initiation complex is open, the first ribonucleotide is brought into the active site to initiate the polymerization reaction in the absence of a primer . This generates a nascent RNA chain that forms a hetero - duplex with the template DNA strand . However, before entering the elongation phase, polymerase may terminate prematurely and release a short, truncated transcript . This process is called abortive initiation . Many cycles of abortive initiation may occur before the transcript grows to sufficient length to promote polymerase escape from the promoter . Throughout abortive initiation cycles, RNA polymerase remains bound to the promoter and pulls downstream DNA into its catalytic cleft in a scrunching - kind of motion . </P>

During the process of transcription in a eukaryote