MBB 222 Lecture Notes - Lecture 29: Leucine Zipper, Coiled Coil, Regulatory Sequence
20 Dec 2018
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Document Summary
Dimers can be homologous (identical -helices) or heterologous (2 different -helices) Unlike prokaryotic genomes, which use both positive and negative regulation to activate and/or repress transcription, eukaryotic genomes are mostly positively regulated. The presence of chromatin means that most promoters are inaccessible to polymerases - this acts as a type of repression, so negative regulation by protein repressors is not necessary. Initiation of transcription almost always requires the action of multiple activator proteins. In order for transcription to proceed, an active rnap ii complex must formed at the promoter (i. e. , rnap ii plus the tfii"s). This requires the action: (1) histone modifying enzymes and chromatin remodeling proteins to expose the dna to be transcribed, and (2) regulatory proteins to promote transcription. Tfiia-h"s form the functional transcription complex and are necessary for transcription of all mrnas whereas activators bind to enhancer elements and enhance transcription levels for specific genes (note that activators are sometimes also referred to as transcription factors)
