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Enhancers and Silencers
Cis-acting DNA sequencesEnhancers: stimulate; Silencers: inhibitUpstream or downstreamClose or thousands bp from promoter
DNA response elements: activators-binding sitesOn either strand of DNA
Bending of enhancer DNA allows activators(specific TF) to interact with:
General TF and RNA polymerase II
Enhancers and Silencers
Cis-acting DNA sequencesEnhancers: stimulate; Silencers: inhibitUpstream or downstreamClose or thousands bp from promoter
DNA response elements: activators-binding sitesOn either strand of DNA
Bending of enhancer DNA allows activators(specific TF) to interact with:
General TF and RNA polymerase II
The Lac OperonOperon:
Coordinately expressed genesStructural and their regulatory genes
Lac operon: (For E. coli catabolism of lactose)
Structural genes: code for 3 enzymes:Lac Z gene: β-galactosidaseLac Y: permeaseLac A: thiogalactoside transacetylase
Regulatory Sequences: Promoter (P) region Operator (O) site CAP-binding site LacI gene: repressor protein
The Lac OperonOperon:
Coordinately expressed genesStructural and their regulatory genes
Lac operon: (For E. coli catabolism of lactose)
Structural genes: code for 3 enzymes:Lac Z gene: β-galactosidaseLac Y: permeaseLac A: thiogalactoside transacetylase
Regulatory Sequences: Promoter (P) region Operator (O) site CAP-binding site LacI gene: repressor protein
Posttranscriptional Modifications
The rRNA and tRNA:Both pro- and eu-karyotes
The mRNA:Only eukaryotes
Posttranscriptional
Modifications: The rRNA
Ribonucleases
Site: Nucleolus
Protein association: Before and during modifications
e 5 S rRNA:
Separate modification
Posttranscriptional Modifications: The
tRNA - 11. Ribonucleolytic cleavage:
16-Nucleotides at 5’-end2 Uracil at 3’-end14 Nucleotides (intron) at anticodon loop
2. Addition of CCA at 3’-endNucleotidyltransferase
3. Base modifications
Posttranscriptional Modifications: The
euokaryotic mRNA - 1
1. 5’- Capping: 7-Methyl-guanosine
2. 3’- Poly-A tail
3. Removal of introns and splicing of exons
Posttranscriptional Modifications: The
euokaryotic mRNA - 2Cap: 7-Methylguanosine triphosphate
Bond: Unusual 5’-5’ triphosphate
Site: Nucleus & cytoplasm
Enzymes: Nuclear guanylyltransferase Cytoplasmic methyl transferase Methyl donor: SAM
Functions: Initiation of translation Stabilizes mRNA
Posttranscriptional Modifications: The
euokaryotic mRNA - 33’- Poly-A tail: 40 – 200Exception: mRNA for histones and interferons
Enzyme: Nuclear polyadenylate polymerase
Site: Nucleus & cytoplasm
Signal: AAUAAA
Functions:Stabilizes mRNAFacilitates its exit from nucleus
Poly-A tail: Shortened after mRNA enters cytosol
Posttranscriptional Modifications: The
euokaryotic mRNA - 5Removal of introns and splicing of exons:
Exons: Coding sequences for proteins
Spliceosome: Binding of snRNPs & primary transcriptCorrect alignment of neighboring exonsallows splicing of exons
The snRNPs: snRNAs + proteins
Introns: Sequences not coding for proteinsNo, few or many introns/mRNA
Posttranscriptional
Modifications: The
euokaryotic mRNA - 5
Systemic lupus Erythematosus:Auto Abs against snRNPs
β-Thalassemia:Splice site mutations
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