Positive-transcription elongation factor

Zhou J, Zhou S (2010) Berberine regulates peroxisome proliferator-activated receptors and positive transcription elongation factor b expression in diabetic adipocytes. Eur J Pharmacol 649(l-3) 390-397... 

Cyclin T-CDK9 (review Simone and Girodano, 2001) functions as a positive transcription factor during transcription elongation of RNA polymerase II by phosphor-ylating the CTD. The HIV regulatory protein Tat binds to and specifically activates the cyclin T-CDK9 complex. 

Recent results indicate that the association of RNA splicing factors with the phosphorylated CTD also stimulates transcription elongation. Thus chain elongation Is coupled to the binding of RNA-processing factors to the phosphorylated CTD. This mechanism may ensure that a pre-mRNA is not synthesized unless the machinery for processing it is properly positioned. 

Termination positions are defined by the thermodynamic stability of the polymerase complex, whereas the efficiencies of termination are determined by a kinetic competition between RNA elongation and release at each position (94). The termination efficiency is affected mostly by the strength of the stem—loop, the presence of the U-tract, and also by the concentration of NTP substrates. The efficiency of transcription termination also depends on other factors such as the size and shape of the hairpin, not just its stability, most likely involving interactions with the polymerase. Different RNA hairpins exert varying effects on transcription termination, while a cruciform structure may have no or some attenuating effect on transcription. Furthermore, certain changes in the stem sequence designed to maintain or raise the stability of the stem (AG = —18 kcal/mol) lead to a decrease... 

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