The enzyme activities exhibited by some of the subunits of TFIIH are known

The enzyme activities exhibited by some of the subunits of TFIIH are known

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The enzyme activities exhibited by some of the subunits of TFIIH are known: 2 subunits exhibit helicase activity 1 subunit exhibits protein kinase activity (phosphorylates proteins) The helicase activity of TFIIH is thought to unwind the DNA at the start site of transcription The protein kinase activity is thought to cause the RNA polymerase II to leave the promoter so elongation can occur. TFIIH seems to phosphorylate specific amino acid side chains in the RNA polymerase II (introduces negative charges!) and this seems to provide the force to disrupt the strong interaction between the initiation complex and the polymerase. Not all promoters for RNA polymerase II contain a TATA box. A second important sequence element was found in many polymerase II promoters called initiator sequence ( Inr ). Inr can represent the only specific sequence in a
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Unformatted text preview: polymerase II promoter or it can occur together with a TATA box. Inr is recognized by other subunits of the TFIID complex (the TAFs ) and transcription proceeds in the same order as described before. But although in the Inr case TBP does not provide the specific binding, it is none-the-less required as part of the TFIID complex for transcription to occur and therefore seems to play a central role in initiation . From in vitro to in vivo (in the living cell) ? Much of the transcription process by RNA polymerase II still needs to be elucidated. For example, the function of many of the basal transcription factors is not known. And the way transcription actually occurs in the living cell could still be different from the way it occurs in the test tube ....
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This document was uploaded on 11/03/2011 for the course BIOLOGY MCB2010 at Broward College.

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