Final answer:
TF2H is a subunit of the transcription initiation complex that contains the XPD helicase subunit, which helps in unwinding DNA and facilitating RNA polymerase II during transcription initiation.
Step-by-step explanation:
The student's question pertains to a component of the eukaryotic transcription initiation machinery. The TF2H subunit, mentioned in the question, is part of the transcription initiation complex that mediates access to the template DNA strand during transcription. TF2H is a multifunctional protein complex that contains several subunits involved in unwinding DNA and phosphorylating the RNA polymerase II C-terminal domain (CTD), which is necessary for the initiation of transcription. One important subunit of TF2H is the XPD (also known as ERCC2) helicase, which is essential for the movement along with the template strand. TF2H, in collaboration with other transcription factors like TFIIA and TFIIB, allows RNA polymerase II to begin synthesizing mRNA.