Class A activity alone specifies sepals.

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.

TLS Online TPP Program

#Id: 6500

#Unit 3. Fundamental Processes

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: 6501

#Unit 3. Fundamental Processes

The phosphorylation pattern on the CTD is dynamic during the elongation process, catalyzed and controlled by multiple protein kinases, including P-TEFb, and phosphatases. Most oft the basal transcription factors are released from the promoter at this stage.

TLS Online TPP Program

#Id: 6502

#Unit 3. Fundamental Processes

Sites of phosphorylation on the CTD serve as a recognition or anchor point for other proteins to dock with the polymerase. The capping enzyme (guanylyl transferase), which adds the G residue to the 5' end of newly synthesized mRNA, binds to CTD phosphorylated at serine 5, the first phosphorylation event catalyzed by TFIIH. 

P-TEFb leads to recruitment of a set of proteins called SCAFs to the CTD, and they in turn bind to splicing factors. This may be a means of coordinating transcription and splicing.