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TLS Online TPP Program

#Id: 9584

Jurassic- First birds and angiosperms

#Unit 11. Evolution and Behavior #The Geological Time Scale #Part B Pointers
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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.
TLS Online TPP Program

#Id: 6503

#Unit 3. Fundamental Processes

These two mechanisms, (1) binding of the capping enzyme to RNA polymerase II specifically through its unique CTD phosphorylated on serine 5 of the heptapeptide repeat during transcription initiation by TFIIH, and (2) activation of the capping enzyme by the serine 5–phosphorylated CTD, result in specific capping of RNAs transcribed by RNA polymerase II.
TLS Online TPP Program

#Id: 6504

#Unit 3. Fundamental Processes

Once bound to Pol II, Ptefb phosphorylates the serine residue at position 2 of the CTD repeats. That phosphorylation event correlates with elongation. In addition, P-TEFb phosphorylates and thereby activates another protein, called SPT5, itself an elongation factor. Finally, TAT-SF1, yet another elongation factor, is recruited by P-TEFb. Thus, P-TEFb stimulates elongation in three separate ways.
TLS Online TPP Program

#Id: 6755

#Unit 3. Fundamental Processes

Most mRNAs decay stochastically (like the decay of radioactive isotopes), and as a result mRNA stability is usually expressed as a half- life (t½).
TLS Online TPP Program

#Id: 6756

#Unit 3. Fundamental Processes

Method for determining mRNA half-lives.
RNA polymerase II transcription is shut down, either by a drug or a temperature shift in strains with a temperature sensitive mutation in a Pol II gene. The levels of specific mRNAs are determined by northern blot or RT-PCR at various times following shutdown.
TLS Online TPP Program

#Id: 6757

#Unit 3. Fundamental Processes

In E. coli the typical mRNA half-life is about 3 minutes, but half-lives of individual mRNAs may be as short as 20 seconds or as long as 90 minutes.  In budding yeast, mRNA half-lives range from 3 to 100 minutes, whereas in metazoans, half-lives range from minutes to hours, and in rare cases, even days.