pp 19 Flashcards
What is the difference between gene expression in bacterias vs eukaryotes?
Bacteria: no need to export transcript to another location
Eukaryotes: several export mechanisms, posttranscriptional regulation
How is the post-transcription regulated in bacteria?
regulating expression post-transcriptionally like Riboswitch
What is a riboswitch?
RNA structure that binds a ligand and while doing so will change conformation altering the expression, affecting either transcription and or translation
How does a riboswitch regulate?
found on untranslated regions of mRNA and can influence translation as well as transcription. In mRNA, they can trigger self-cleaving ribozyme and mRNA degradation
How do Riboswitches control expression?
highly specific binding of the small-molecule-binding element to target ligand, which triggers confomational change in the regulatory region altering the structure of the RNA
How do riboswitches inhibit transaltion?
Translation riboswitch binding of ligand results in a change in RNA conformation that blocks RBS
How do riboswitches activate translation?
Translation riboswitche binding of the ligand results in a change in RNA conformation that activates RBS
What is TPP riboswitch?
Thiamine pyrophosphate riboswitch
What does TPP riboswitch do?
controls post-transcriptional regulation of thiamine biosynthesis genes, without TPP ligand, the RNA can be digested by RNase, so it would be degraded.
What does the glmS gene code for?
an enzyme involved in sugar metabolism, generating glucosamine 6-phosphate
How does the glmS riboswitch trigger mRNA cleavage?
5’ untranslated of glmS gene included a riboswitch that binds to GlcN6P, resulting in a change in conformation triggering RNA slef-cleavage (ribozyme activity) once cleaved. promoting degradation
What is required for the initiation of translation in eukaryotes?
several eukaryotic initiation factors (eLFs)
What regulatory mechanisms occur after transcription in eukaryotes?
- transcripts are routinely proceed and not immediately translated
- mRNA’s can be stored and translated later (allowing more rapid response to cellular needs or signals)
What are the steps of initiation with the eLFs
- GTP bound eLF2 delivers initiator methionyl-tRNA to the P site of 40S ribosomal subunit with hydrolysis of GTP
- Recycling of GDP-eLF2 to GTP-eLF2 involves eLF2B but is prevented by phosphorylation
- Translation of proteins can be regulated by phosphorylation of eLF2 through signal transduction
What is required for translation initiation?
Recruitment of eukaryotic initiation factors elF4E and eLF4G at the 5’ UTR
What is required to recruit elF4G?
coordinated interaction with elF4E at 5’ UTR and poly(A) binding protein (PABP) at the 3’ poly (A) tail
What does the binding of elF4E and PABP form?
loop or circularized mRNA structure that facilitates recruitment of other translational regulators and ribosomal subunits for translation initiation
What is a common form of post-transcriptional control of gene expression?
involving a seuqence of elements in 5’ or 3’ UTR that binds proteins affecting mRNA stability and translatability
What is transferrin?
Iron binding protein used to carry iron from outside cell into cell
What is transferrin receptor (TfR)
Transfers iron-bound transferrin into the cell. mRNA relatively high with low iron levels (mRNA degraded) and mRNA relatively low with high iron levels.W
What is ferritin?
Iron binding protein used to sequester iron within the cell
What is the iron response in elements?
Binding of a protein to a sequence called an iron response element in the 5’ or 3’ UTR can either enhance the stability or an mRNA (protecting from cleavage) or block translation. The stability of TfR mRNA is enhanced by protein binding to the 3’ IRE. Translation of ferritin is blocked by binding to the 5’ IRE
What do iron response elements at the 5’ UTR of ferritin mRNA and 3’ UTR of TfR mRNA contain?
Stem loops with conserved sequences
How do the electrophoretic mobility shift assay shpw cell proteins binding IRE?
unlabeled RNA as competitor for protein binding Lane 1: No competitor. Lane 2: unlabeled ferritin mRNA. Lane 3: unlabelled TfR mRNA. Lane 4: unlabeled B-globin mRNA
What are the proteins binding IREs?
Iron regulatory proteins (IRP)
What are IRPS
proteins that bid to iron response elements (IREs) when iron is low
What does binding or IRPS to IREs result in when referring to mammals?
Blocks production of proteins that use and store iron (ferritin) while promoting production for proteins for iron uptake (transferrin receptor)
