James 4 7 7 Submit yourselves therefore to
James 4: 7 7 Submit yourselves therefore to God. Resist the devil, and he will flee from you. © 2000 Timothy G. Standish
Regulation of Transcription Timothy G. Standish, Ph. D. © 2000 Timothy G. Standish
Eukaryotic RNA Polymerase II Promoters � Eukaryotic promoters are made up of a number of sequence elements spread over about 200 bp upstream from the transcription start site � In addition to promoters, enhancers also influence the expression of genes � Control of gene expression in eukaryotes involves many more factors than control in prokaryotes � This allows much finer control of gene expression © 2000 Timothy G. Standish
Eukaryotic Promoters 5’ Promoter Exon 1 Sequence elements TATA ~200 bp Some sequence elements are also response elements © 2000 Timothy G. Standish
Response Elements �Response elements are short sequences found either within about 200 bp of the transcription start site, or as part of enhancers �Different genes have different response elements �Binding of transcription factors to response elements determines which genes will be expressed in any cell type under any set of conditions © 2000 Timothy G. Standish
Heat Shock Response Elements � Sudden changes in the temperature of cells cause stress in response to which heat shock genes are expressed � At least some heat shock genes are thought to be chaperones that help proteins fold correctly � Heat shock genes have Heat Shock Elements (HSEs) in their control regions � Heat Shock Transcription Factors (HSTFs) bind the HSEs up regulating expression of heat shock gene products © 2000 Timothy G. Standish
The Heat Shock Response Hot HSTF Kinase Cool Heat shock genes Heat shock response elements © 2000 Timothy G. Standish
The Heat Shock Response Hot HSTF Kinase Cool Activation of kinase Phosphorylation of HSTF Heat shock response elements © 2000 Timothy G. Standish
The Heat Shock Response Hot Activation of HSTF Kinase HSTF Cool Transcription initiation of all heat shock genes with HSEs Heat shock response elements © 2000 Timothy G. Standish
Metallothionein Regulation � Heat shock protein regulation illustrates how a group of genes can be regulated by a single transcription factor � Other genes are regulated by a group of transcription factors which allows them to either respond to multiple separate situations, or respond only to a specific combination of situations � Metallothionein is an example of a gene that can be turned on by multiple transcription factors © 2000 Timothy G. Standish
Metallothionein Regulation Glucocorticoid Response Element - Behaves as an enhancer and allows regulation by steroids GRE BLE MRE TGACTCA A consensus sequence to which AP 1 binds conferring a response to phorbol esters MRE BLE TRE MRE GC MRE TATA -260 -240 -220 -200 -180 -160 -140 -120 -100 -80 -60 -40 -20 Basal Level Elements (needed for transcription, act as enhancers) Metallothionein Regulator Elements - Multiple copies confer greater levels of induction by heavy metals Constitutive Elements © 2000 Timothy G. Standish
�A Regulation By TFs single transcription factor (or group of transcription factors) may regulate expression of a group of genes (i. e. , heat shock proteins) �A single gene may be regulated by a number of independent transcription factors (i. e. , metallothionein) �Eukaryotic regulation does not seem to involve repression �To achieve high levels of expression, several different transcription factors binding to different response elements may be necessary © 2000 Timothy G. Standish
�Some How Do TFs Recognize Response Elements? mechanism must exist for protein transcription factors to recognize the specific sequences of bases found in response elements �There is no known specific relationship between a given amino acid and a base that would allow direct recognition �Groups on bases that are not involved with base pairing have the potential to be recognized by proteins �Some specific sequences are known to influence the gross structure of DNA © 2000 Timothy G. Standish
DNA Binding Domains �Transcription factors exhibit a number of different motifs found in the area known to bind DNA: �Zinc finger -First found in TFIIIA �Helix-turn-helix - First described from phage receptors �Amphipathic Helix-loop-helix - Identified in some development regulators �Leucine zipper - Held together by interactions between leucine amino acids © 2000 Timothy G. Standish
�Are Zinc Fingers found in steroid receptors and are common in other transcription factors �Interaction between cysteine and histidine amino acids and the divalent zinc ion results in the formation of loops called “fingers” �One side of each loop forms an a-helix which can lie in the major grove of DNA �Interaction between the amino acids in the zinc finger and bases in the DNA allow for sequence recognition © 2000 Timothy G. Standish
Zinc Fingers O O H 2 N C C H OH C H H C HS H 2 N N H N C © 2000 Timothy G. Standish
Zinc Fingers ≈6 Amino acids C H Zn++ C H 2 - 4 Amino acids C H Zn++ C H ≈ 23 Amino acids C H Zn++ C H 7 - 8 Amino acid linker © 2000 Timothy G. Standish
© 2000 Timothy G. Standish
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