TLS Online TPP Program

#Id: 6494

#Unit 3. Fundamental Processes

Model of Formation of the DABPolF Complex

TLS Online TPP Program

#Id: 6495

#Unit 3. Fundamental Processes

TFIIB, TFIIE, and TFIIH are required to melt DNA to allow polymerase movement. The last factors to join the initiation complex are TFIIE and TFIIH. 

TLS Online TPP Program

#Id: 6496

#Unit 3. Fundamental Processes

TFIIH is the only general transcription factor that has multiple independent enzymatic activities. Its several activities include an ATPase, helicases of both polarities, and a kinase activity that can phosphorylate the CTD tail of RNA polymerase II (on serine 5 of the heptapeptide repeat). TFIIH is an exceptional factor that may also play a role in elongation.

TLS Online TPP Program

#Id: 6497

#Unit 3. Fundamental Processes

On a linear template, ATP hydrolysis, TFIIE, and the helicase activity of TFIIH (provided by the XPB and XPD subunits) are required for polymerase movement. This requirement is bypassed with a supercoiled template. This suggests that TFIIE and TFIIH are required to melt DNA to allow polymerase movement to begin. To extend elongation into the transcription unit, a kinase complex called P-TEFb is required. P-TEFb contains the CDK9

kinase, which is a member of the kinase family that controls the cell cycle. P-TEFb acts on the CTD to phosphorylate it further on serine 2 of the heptapeptide repeat.

TLS Online TPP Program

#Id: 6498

#Unit 3. Fundamental Processes

TLS Online TPP Program

#Id: 6499

#Unit 3. Fundamental Processes

RNA polymerase II terminates after a short distance; small oligonucleotides of 4–5 nt are unstable; crystal structures of these RNA/DNA hybrids are unordered. Only longer hybrids have proper base pairing. The short RNA products are degraded rapidly. The suggestion is that this abortive initiation is a form of promoter proofreading.