Eukaryotic Gene expression Flashcards
what is control used for in euk gene expression?
regulate the genetic program that underlies embryonic development and tissue differentiation; gene expression patterns must remain permanent, even for decades–>activating signals may be transient
what ar ethe RNA pols in a euk?
Pol I, Pol II, and Pol III
what is the role of Pol II?
similar to bacterial RNA pol; transcribes the majority of protein coding genes and microRNAs
what is the role of pol I?
transcribes for larger ribosomals RNA
what is the role of pol III?
transcribes short RNAs such as 5S rRNAs and tRNAs
each euk pol has more than just single sigma TF–alows for much more intricate gene control and need to displace chromatin
ya
7 additional subunits attach to RNA pol II
ya
what is the purpose of TFIID?
various subunits of it recognize the TATA, INR (initiator) and DPE (downstream promoter element) seq domains
what composes TFIID?
12 subunits (human), including the TBP (TATA binding protein)
what is the point of TBP?
to bind TATA in the minor groove at the con seq TATA(A/T)A(A/T)
what is the purpose of BRE?
a sequence upstream of the TATA box for which TFIIB binds to
what is TFIIB?
basal factor; binds BRE; binds both TFII-D and pol–>brings pol to promoter; gives polarity since the TATA box is symmetrical
what is the purpose of TFIIA?
stabilizes the binding of TFIIB
what is the purpose of TFIIF?
stabilizes the binding between TFIIB and RNA pol II
genes aren’t in a total on/off state, but the rate of transcription can be increased or decreased
ya
what is the purpose of the mediator complex?
integrates signals of whether a gene needs to be up- or down-regulated; it brings the Pol II complex to wherever it’s needed–>these signals increase or decrease; allows for long-range control (through bending of DNA); can also integrate multiple signals by binding to many different places on DNA–>the different signals may increase transcription by 20%, others may inhibit by 40%, etc
TFIIS role
elongation factorl; keeps pol II from stalling, has proofreading activity, stimulates hydrolysis of incorrect rNTPs
purpose of introns?
allows for multiple RNA forms to arise from one gene
we can possible judge organism complexity based on number of introns
ya
what is the role of GT/MT?
guanylyn transferase/methyl transferase; needed for capping
What is the purpose of TFIIH?
helicase (requires TP) /kinase–phosphorylate other proteins in the complex; required for expression of some genes–creates the bubble to allow RNA synth
what is the role of P-tef-B
modifies Pol II tail to release the initiation complex; (involved in elongation)
what is the role of CstF and CPSF?
cut 35 bases after AAUAAA
what does PAP do?
add the poly-A tail
what is the purpose of PAB?
acts a ruler and binds As to set the length of the tail
what is the purpose of TFIIE?
recruits TFIIH
what is the heptad con seq in the C term domain of pol II?
Tyr-Ser-Pro-Thr-Ser-Pro-Ser; ser5 phos. RNA pol 2 for activation by a subunit of TFIIH; pTEFb transitionsRNA ol phos to ser2 (and dephos of ser 5 by phosphatases) as it moves through the gene
why is RNA capping used, and what happens?
to improve stability of mRNA, as exonuclease has a substrate specificity for 5’ ends of RNA/DNAs
Step 1: 5’5’ bond between 5’ end of mRNA and guanine is catalyzed by guanylyl transferase
Step 2: Guanine cap is methylated by guanine-7-methyl transferase
most plants and animals can also methylate the 2’ carbon of deoxyribose of the +1 nuc and vertebrates can methylate 2’ of 2+ nt
ya
what creates the polyA tail?
cleavage stimulation factor (CstF) and CPSF (cleavage and polyadenylation specificity factor); PAP then works much more quickly when CstF and CPSF o their job–can add up to 250 As
what signals may termination utilize?
2 signals: 1. Lack of CstF and CPSF attached to pol II tail (CTD tail)–antitermination factors–and possibly promoting other binding factors to leave (termination factors)
2. 5’ end of the cleaves mRNA now has no cap–5’3’ mRNA exonuclease (Xnr2)
