Lecture 2 Flashcards
What is the difference in transcription in prok vs euk?
Txn in euk - takes place on DNA that is wrapped in chromatin
What is needed in chromatin for txn to proceed?
Chromatin must be open for gene to be activated
What is epigenetic regulation of gene expression?
Chromatin-mediated regulation
What is heterochromatin?
Regions of the chromosomes where the DNA is more densely packed (wrapped in nucleosides), it is rich in repetitive DNA (transposons, centromeres and telomeres), it is not accessible to transcriptional machinery, inactive genes are found in heterochromatin
What is euchromatin?
Active genes are found in euchromatin
What are the three RNA pols that eukaryotes have?
RNA pol I - synthesizes pre-rRNA (ribosome components, protein synthesis)
RNA pol II - synthesizes mRNAs (encodes protein), snRNAs (splicing), siRNAs (chromatin mediated repression/tln control), miRNAs (tln control)
RNA pol III - synthesizes tRNAs (protein synth), 5S rRNA (ribosome component/protein synth), snRNA U6 (RNA splicing), 7S RNA (signal recognition particle for insertion of polypeptides into the ER), other small stable RNAs (various functions)
How many polypeptides is RNA pol II are there?
12 polypeptides, RPB1-RPB12
What are the structures of the RNA pol II?
There are 5 subunits, Clamp domain in the polymerase accommodates DNA, after positioning over DNA the clamp is closed by a bridge, the synthesis of RNA takes place in the catalytic center with the participation of Mg++, the synthesized RNA exits through a “channel” and is immediately capped by 7m guanosine
How do you maintain the structure of RNA pol II?
Need to crystallize structure to maintain it
What is the CTD?
Carboxylic terminal domain - a unique domain in the RPB1 subunit, not found in other polymerase, it is involved in multiple regulatory interactions and plays key roles initiation, release, elongation, and processing of the synthesized mRNAs
What is special about the Ser residues on the CTD?
They are targets for protein kinases, they are phosphorylation upon transition from initiation to elongation
What are core promoter sequences?
The RNA pol II transcribed genes are regulated by these core promoter sequences, also known as conserved basal promoter elements
What are the 4 core promoter elements?
BRE - TFIIB recognition element, GC rich
TATA box - TFIID associates with TATA box, has a tight consensus sequence, prevalent in highly transcribed genes
Inr- Initiator, less conserved
DPE - Downstream promoter element, not highly conserved, regulates initiation of txn, influence activity of promoter
Where does transcription start?
Initiation site, usually A on the coding strand, RNA pol’s must recognize the promoter and correctly initiate txn at a very specific position, which they can’t do alone, done through GTFs
What are GTFs?
General Polii transcription factors assemble the so called pre initiation complex over the core promoter sequences
