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Molecular Biology: Prokaryotic and Eukaryotic Transcription


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experimental method for studying prokaryotic RNA polymerase (133)
1. isolate protein
2. separate subunits with SDS-PAGE
list the prokaryotic RNA polymerase subunits (133)
1. 2 alphas
2. beta
3. beta prime
4. omega (not easily isolated)

5. sigma
experimental method for separating sigma from other prok. RNA polymerase subunits (133)
subject the RNA pol holoenzyme to ion exchange chromatography with neg-charged phosphocellulose resin.
experiment to determine if sigma subunit of RNA polymerase is responsible for binding promotors (137)
1. isolate core and holoenzyme
2. bind to labeled promoter DNA (lambda genomic DNA)
3. add excess unlabeled DNA (so that any DNA that dissociated would bind to this instead of labeled DNA)
4. measure dissociation rate of DNA-polymerase

found that the core enzyme dissociated from DNA at a much higher rate than the holoenzyme, meaning the latter binds DNA much tighter
experiment to determine if prokaryotic RNA polymerase binds better at higher temperatures (137)
1. formed complexes between RNA pol holoenzyme and labeled DNA at three different temperatures.
2. added unlabeled DNA
3. removed samples at various times and passed them through nitrocellulose

complex was much more stable at higher temperatures, implying that local DNA melting occurs when pol is bound tightly to promoter
experiment to determine how much local melting occurs at the prokaryotic transcription bubble
METHOD: methylation S1-assay
1. use end-labeled promoter DNA
2. allow RNA pol to bind
3. treat with DMS which methylates at ss adenines
4. remove polymerase
5. treat with SDS under mild conditions
6. denature fragments and electrophorese

found that a region of ~10-12 bp was denatured
open promoter complex (gloss)
complex formed by tight binding between pol and promoter. Open in the sense that approximately 10 bp separate
closed promoter complex (gloss)
complex formed by relatively loose binding between pol and promoter. Closed in the sense that the DNA duplex does not open up.
core promoter elements
-10 box: TAtAaT

-35 box: TTGACa
consensus sequences (138)
average of several similar sequences. When perfect matches to consensus sequences are found, they tend to occur in very strong promoters that initiate transcription unusually actively. (up and down mutations look more and less like consensus sequences, respectively)
UP element (139)
Found 40 to 60 positions upstream of promoter

not always present

recognized by alpha subunits
alpha subunit of prokaryotic RNA polymerase (152)
to study, used alpha-subunit mutations (truncations, deletions, site-directed mutagenesis)
confirmed binding with DNase footprinting
found that it is the CTD that contacts the UP element
CTD of prokaryotic RNA polymerase (154)
is an independently folded CTD that recognizes and binds to a promoter’s UP element.

since RNA pol will bind to a promoter with an UP element with both its sigma and alpha subunits, UP elements allow very strong interaction between the two and thus high rates of transcription.
Fis sites (139)
enhancers that are found at strong promoters between positions -60 and -150

binding site for the transcriptional activator Fis

does not bind RNA pol itself
sigma subunit of prokaryotic RNA polymerase (140)
stimulates initiation of transcription and can be reused
experiment to determine how transcription initiation occurred (is there any elongation?) (140)
1. allowed RNA pol to synthesize 32P-labeled RNA in vitro using prokaryotic promoter + heparin + other nucleotides
2. electrophorese

found many small bands at bottom of gel: indicated that the polymerase made many small (9-10nt), abortive transcripts without ever leaving the promoter
heparin (140)
prevents reassociation between DNA and polymerase released at the end of a cycle of transcription
steps in transcription initiation (L 1)
1. closed promoter complex: RNA pol binding to DNA
2. open promoter complex: sigma stimulates pol to convert to open complex
3. polymerizing first few nucleotides while polymerase remains at the promoter
4. promoter clearance: transcript forms stable hybrid with template (pol clears promoter, loses sigma, begins elongation)
experiment to determine what sigma subunit does (141)
1. run two reactions: one with RNA with 14C-ATP label (incorporates through all RNA), one with RNA with gamma-32P-GTP end label (incorporates only in 1st position of RNA)

appears that sigma contributes to both initiation and elongation, but initiation is rate limiting
experiment to determine if sigma subunit activates initiation (141)
1. allow initiation to occur and then add rifampicin
2. ultracentrifugate
3. measure RNA chain length in presence and absence of sigma

found sigma made no difference in length of RNAs, thus it does not contribue to elongation, just initiation
experiment to determine that sigma subunit is reused (142)
1. allowed pol to initiate and elongate RNA chains at low ionic strength, so that pol couldn't dissociate from template to start new RNA chains.(chains measured by gamma-32P-NTP labels)
2. then added new rif-resistant core pol in presence and absence of rifampicin.

immediate rise of both curves showed addition of core polymerase can restart RNA synthesis implying that sigma was reused. The fact that both curves increased means rif-resistance comes from core, not from sigma
rifampicin (141)
blocks prokaryotic transcription initiation, but not elongation
experiment to determine if sigma subunit is bound to core polymerase (143)
trailing edge: fluorescence acceptor attached to 5' end of DNA. FRET efficiency decreases as txn occurs because pol gets farther from 5' end.

leading edge: fluorescence donor attached to 3' end. FRET efficiency is low at first, but will increase if sigma stays attached to core enzyme. Will not increase if sigma dissociates

found that FRET increases, so sigma does not dissociate. It is loosely bound to the core enzyme
FRET (fluorescence resonance energy transfer)(143)
used as a measure of the proximity of 2 fluorescent proteins relative to each other

if the donor and acceptor proteins are within 10nm, an excited donor will transfer E to the acceptor
Determinants of UP element strength (Ross paper)
1. relative affinity of the sequence for the alpha subunit
2. exact positioning of sites with respect to other promoter elements
3. extent to which a core promoter mechanism is rate-limited at a step affected by alpha-subunit—DNA interaction (e.g., lac UV5)
UP element as defined by Ross et. al
a sequence that increases transcription 2-fold or more in vivo.
further experiments performed to evalutate sigma's associations with the polymerase core enzyme (Bar-Nahum) (144)
1. formed complexes between holoenzyme and promoter + 3/4 nucleotides to allow pol to move to position +32.
2. purify complex with oligos complementary to RNA transcript (beads)
3. release complex with nuclease, SDS-PAGE, immunoblot to identify proteins

shows sigma is less tightly bound during elongation
elongation of transcription (L2)
core extends ribonucleotide chain one ribonucleotide at a time

transcription bubble moves with RNA pol, maintains same approx. size (~17bp)

9bp transcript in RNA-DNA hybrid
example of an intrinsic terminator (prokaryotes) (172)
E. coli trp operon
2 features of intrinsic terminators (172)
1. string of T's in non-template strand: causes RNA pol to pause, allowing hairpin to form
2. inverted repeat just upstream of this: destabilizes the weak rU-dA pairs so that pol is ripped away from the RNA/DNA hybrid
experiment showing if transcription termination worked or not (172)
METHOD: in vitro run-off assay
1. digest trp with HpaII and transcribe frag with trp attenuator in vitro
2. electrophorese products

If attenuation works, should see a shorter (140nt) transcript. If it doesn't, should see longer (260nt) transcript.
transcription termination: what happens when the string of T's at attenuator is mutated?
see more of the longer transcript because non rU-dA bonds are harder to break apart
transcription termination: what happens when iodo-CTP is substituted for CTP?
since iodo-CTP forms a stronger bond with G, the hairpin is stabilized and thus, you see more short product.
transcription termination: what happens with inosine is substitued for G?
since inosine only forms 2 H-bonds with C, it weakens the hairpin and thus, you see more of the longer product.
NusA protein
the core polymerase has an upstream binding site that binds to part of the hairpin, slowing down hairpin formation.

NusA loosens the association between upstream binding site and hairpin, thus promoting termination.
experiment to see how rho affects transcription
1. performed in vitro transcription with gamma-32P-GTP (just initiation) and 3H-UTP (total RNA)
2. add increasing amounts of rho

rho has little affect on initiation, but decreases total amount of RNA. Thus, probably terminates transcription.
experiment to determine if rho acts as a nuclease (176)
1. allowed RNA pol to transcribe in absence of rho. Labeled RNA with 3H-UTP and ultracentrifugated
2. repeated this except using 14C-labeled RNA in the presence of rho + 3H-labeled RNA, then ultracentrifugated

14C labeled transcripts were found near the top of the gradient, indicating they were relatively small, but the 3H transcripts were bulky and the same size as they were originally. Thus, rho has no effect on the size of previously-made transcripts; only affects those made in its presence.
experiment to determine if rho releases RNA product from DNA template (176)
1. transcribed DNA in the same method of other expt (fig. 6.54) in the absence and presence of rho.
2. subjected 3H labeled product to centrifugation

found that the RNA made in absence of rho cosedimented with DNA whereas that made in the presence of rho sedimented independently of DNA. Thus, transcription with rho releases transcripts from DNA template.
properties of rho (177)
an essential protein

a hexamer of identical subunits, each of which has an RNA-binding domain and an ATP-hydrolysis domain.

is an ATP-dependent helicase (propels rho down RNA 5'-->3')

C-rich, G-poor

can move faster than RNA pol, allowing it to catch up
position of rho loading site (177)
binds upstream of termination site at a sequence 60-100 nt long rich in C residues

the longer this region, the more efficient rho is
antitermination (Yarnell paper)
when the transcript is not released as usual (read through transcription occurs)
a protein that binds to the transcription complex and prevents termination and pausing.

It works by speeding RNA to the termination release site before mechanics of release are completed. Alternatively, it could stabilize the complex against the hairpin by inhibiting pausing in region of release.
experiment used to assay binding between lac operator and repressor (189)
1. label lac operon DNA with 32P and add increasing amounts of lac repressor in presence or absence of IPTG (inducer).
2. assay binding via binding with nitrocellulose. Only labeled DNA bound to repressor will attach to filter.

found that repressor-operator interaction worked normally
experiment that shows the lac operator binds to the lac repressor (189)
1. performed lac operator-repressor binding assay (figure 7.6) using 3 different DNAs: wt, one with an operator that doesn't bind repressor well, one with ns DNA

showed that a higher concentration of repressor was needed to achieve full binding with the mutated operator than with wild type, showing that the repressor binds to the operator.
Pastan's experiment with lac repressor (189)
1. added dsDNA + RNA pol + repressor + NTPs
2. add IPTG + rifampicin

found that transcription still occurred, implying that the repressor did not block access by RNA pol to promoter
2 models for repression (189)
1. repressor blocks RNA pol's access to the promoter (competition between repressor and pol)

2. repressor blocks transition from transcriptional initiation state to elongation state (open promoter complex forms, but pol never clears the promoter because of repressor binding)
Lee and Goldfarb's experiment with lac repressor (190)
METHOD: run-off assay
1. incubated a DNA frag containing control region + lacZ with repressor for 10 min
2. add RNA pol. Wait 20 min for open promoter complexes to form
3. add heparin + 3/4 NTPs. Then, add labeled NTP in the presence or absence of IPTG.
4. electrophorese

transcription occurred even when repressor bound to DNA before polymerase could. Thus, repressor does not prevent polymerase from binding and forming an open promoter complex

when repressor was bound, shorter abortive transcripts were made (6 nt instead of 9)
Record's experiment with lac repressor (190)
METHOD: in vitro assay
1. form RNA pol-lac promoter complex
2. measure the rate of transcript synthesis in presence of gamma-fluor-labeled UTP: alone, with heparin, or with lac repressor (transcription rate correlates with amount of tagged PP released)

found repressor mimics heparin, inhibiting reinitiation of abortive transcription (blocking dissociated RNA polymerase from reassociating with the promoter)
3 lac operators (191)
O3: -82
O1: +11
O2: +412

removing O1 causes 18-fold decrease in transcription, removing O2 and O3 causes 50-fold decrease, removing all 3 causes 1300-fold decrease

operators function cooperatively
how does the lac repressor bind? (192)
as a tetramer (2 dimers)

each dimer contains 2 DNA-binding regions

the 2 dimers can bind independently to the operator
catabolite repression (192)
repression of a gene or operon by glucose, or more likely, by a catabolite (breakdown product, cAMP) of glucose
CAP (catabolite activator protein) (193)
a protein necessary for lac operon stimulation by cAMP (the two together cause positive control)
experiment that shows beta-galactosidase production is stimulated by cAMP-CAP (193)
1. combined bacterial extracts with increasing concentrations of cAMP and either wt or mutant CAP.

mutant CAP made much less beta-galactosidase, which makes sense since the mutant CAP had less affinity for cAMP. Too much cAMP interfered with beta-galactosidase production.
where does CAP-cAMP bind? (193)
on the activator site, just upstream of the promoter

all activator sites contain TGTGA sequence

everywhere where activators are needed have very weak promoters, scarcely recognizable -35 boxes.
experiment that shows that CAP-cAMP allows formation of an open promoter complex (194)
incubate lac promoter + RNA pol + rifampicin + NTPs in presence and absence of CAP-cAMP

found transcription can occur only in the presence of CAP-cAMP, meaning this complex helps RNA pol form an open promoter complex (since rifampicin won't allow txn unless an open promoter complex is formed)
2 steps in recruitment of RNA pol by CAP-cAMP (195)
1. formation of the closed promoter complex
2. conversion of the closed promoter complex to the open promoter complex
2 promoters in lac operon (195)
P1: strong
P2: inefficient (22 bases upstream of P1)

CAP-cAMP reduced initiation at P2 while stimulating initiation at P1, thus freeing up more RNA pol to bind at P1.
how does CAP-cAMP facilitate binding of RNA pol to the promoter? (195)
CAP-cAMP interacts with pol via the pol's alpha-CTD and bind cooperatively.

evidence: CAP-cAMP and pol cosediment during centrifugation and x-link during DNA-footprinting

X-ray crystallography shows 1 subunit of alpha binds DNA alone and the other binds DNA and CAP.
epitope tagging (276)
genetically alter the sequence of proteins of interest in eukaryotes to include a 9 aa epitope tag. Then subject translated proteins to a monoclonal antibody (specific to the epitope tage) and purify the protein of interest from the rest of the proteins

used in Kolodzie paper to purify RNA pol II
3 forms of RPB1 (279)
IIa: "parent"
IIo: phosphorylated version of IIa
IIb: missing the CTD
how CAP-cAMP binds DNA (195)
CAP-cAMP bends DNA at 100 degree angle, confirmed with DNA mobility assay evidence (bent DNA does not travel as fast as straight DNA--lac DNA digested with RE and bound to CAP-cAMP migrated on gel at different rates, showing it is bent.

confirmed by crystal structure
araO1 (198)
one of the ara operators, responsible for transcription of araC gene (makes a control protein)
araO2 (198)
one of the ara operators, found far upstream of the promoter (-265 --> -294).

controls PBAD
how does araO2 regulate transcription if it is so far upstream of the promoter? (198)
DNA looping

need integral number of loops (multiples of 10.4 bp) because DNA cannot interact with araC binding site if it is twisted 180 degrees.
araC, general (198)
ara control protein

acts as both a positive and negative regulator
how is araC a negative regulator for the ara operon? (198)
in the absence of arabinose, monomers of araC bind to O2 and I1, bending the DNA and blocking access to the promoter by RNA pol
how is araC a positive regulator for the ara operon? (198)
in the presence of arabinose, arabinose binds to araC, causing a conformational change. This causes araC to bind as a dimer to I1 and I2 and not to O2, which opens up the promoter to access by RNA pol. Glucose must be absent/depleted for the operon to work because CAP-cAMP must bind to the CAP binding site to activate transcription.
experiment that gives evidence for the looping model of ara operon repression (200)
1. prepared minicircles containing either wt or mutant araC binding sites
2. added araC to form a complex with labeled DNA, then excess (competitive) DNA containing an araI site as a competitor.
3. electrophoresed to see whether in looped or unlooped form (looped travels faster)

found that looping was inhibited by both the araO2 and araI mutant, demonstrating that both sites are important in binding to araC.

with mutant O2: loop stable for less than 60 seconds
with wt O2: loop stable for more than 90 minutes
experiment that shows that arabinose can break the araC repression loop (200)
1. added arabinose to preformed loops before electrophoresis in the presence and absence of arabinose

found that the loop was broken in the presence of arabinose
methylation interference assay in ara operon (201)
a means of detecting the sites on a DNA that are important for interacting with a particular protein. These are the sites where methylation interferes with binding to the protein.

used to show that after the ara loop opens, the araC monomer bound to araO2 binds to araI2. (araC and araI2 don't interact in looped state)

in assay, the wt araI2 DNA bound to araC in linear state, but not the mutant araI2.
eukaryotic RNA polymerase, 2 types: early notions (272)
early studies revealed there were at least 2 different RNA polymerases
1) one made rRNA genes
2) the other made protein-coding genes
evidence for the eukaryotic RNA pol that makes rRNA genes (272)
ribosomal genes are different than nuclear:
1) they have 60% GC comp, vs. 40%
2) they are repetitive
3) they are found in the nucleolus, mRNA in the nucleoplasm
experiment that showed where eukaryotic RNA polymerases were found (272)
purify with DEAE-Sephadex ion-exchange chromatography

1. II and III found in the nucleoplasm fractions
2. I found in the nucleolus fraction
RNA polymerase I (272)
found in the nucleolus

(large) rRNA-synthesizing enzyme
RNA polymerase II (273)
found in nucleoplasm

makes heterogeneous nuclear RNA (hnRNA) and small nuclear RNA (snRNA)--> leading to mRNA
RNA polymerase III (273)
found in nucleoplasm

makes tRNA and 5S rRNA genes
sensitivity of RNA polymerases to alpha-amanitin (274)
RNA pol II sensitive to a lower concentration of it

RNA pol III sensitive to higher concentrations of it

RNA pol I not sensitive even at high concentrations
effect of alpha-aminitin on small RNA synthesis (274)
synthesized labeled RNA in presence of increasing amounts of alpha-amanitin. Small RNAs leaked out of nucleus and were found in supernatant. PAGE

found that the inhibition of 5S rRNA and 4S tRNA precursor synthesis closely parallels the effect of the toxin on polymerase III (showing polymerase III transcribes these genes)
core subunits of RNA polymerase II (276)
Rpb1: homologous to beta prime (both bind DNA)

Rpb2: homologous to beta (both near active site)

Rpb3: homologous to alpha
common subunits of RNA polymerase II (276)
Rpb5, 6, 8, 10, 12
nonessential subunits of RNA polymerase II (277)
Rpb4, 9: mutants viable at 37 degrees but not at low or high temp. Rpb4 may anchor Rpb7.

deltaRpb4 can still transcribe DNA, but doesn't initiate at native promoter
2 parts of RNA polymerase II promoter (287)
1. core promoter
2. upstream promoter element
components of the RNA polymerase II core promoter (287)
1. TATA box centered at -25
2. TFIIB recognition element (BRE) upstream of the TATA box
3. Initiator centered at transcription start site
4. downstream promoter element (DPE)
RNAi (Wright paper)
interference RNA (dsRNA)

specific to the gene that encodes a protein of interest-->prevents translation

more efficient than knocking out genes genetically and allows one to look at proteins in vivo.
TATA box (287)
consensus sequence: TATAAA (non-template)

centered at -25

no TATA box found in housekeeping (constitutively "on") genes or developmentally-regulated genes (e.g., homeotic genes)
what kind of genes have TATA boxes? (287)
specialized genes encoding tissue-specific proteins
2 functions of TATA boxes (287)
1. positions RNA pol
2. allows transcription to occur

function depends on the gene
experiment showing that TATA boxes are important for positioning RNA pol (288)
1. promoter deletion mutagenesis on SV40 early promoter
2. located initiation sites by primer extension, S1 mapping
3. made series of deletions

found that overall transcript size was proportional to the deletion. Distance between TATA box and transcription initiation sites remained constant (~30bp). Initiation moved to a downstream purine.

when TATA box deleted altogether, transcription started at random sites
experiment showing that TATA boxes are important for transcription to occur (289)
METHOD: linker scanning mutagenesis in herpes virus tk promoter
1. cut DNA with REs and digest the ends so that the DNA is missing about 10 bp
2. fill the gap with synthetic DNA linker
3. repeat with gaps farther and farther down the DNA-->allows one to scan through DNA of interest
4. injected mutated DNA into frog oocytes along with wt-DNA
5. assayed transcription via primer extension

found mutations in the TATA box destroyed promoter activity
DPE (downstream promoter elements) (290)
commonly coupled with initiators in the absence of TATA boxes

just like the TATA box, can bind TBP of TFIID

typically 30bp downstream of start site
initiator of eukaryotic promoter (289)
a site surrounding the transcription start site that is important in the efficiency of transcription from some class II promoters, especially those lacking TATA boxes.

along with TATA box is sufficient for basal transcription
BRE (TFIIB recognition element) (290)
TFIIB binds to promoter with RNA pol and other factors

BRE elements help TFIIB bind
upstream element (2 types) (290)
1. GC boxes: bound by Sp1, a specific transcription factor. Orientation independent, but position-dependent (must be upstream). Found in SV40 promoter.

2. CCAAT box: bound by the CCAAT binding transcription factor (CTF). Found in herpes TK promoter.
first enhancer discovered (296)
that in the SV40 5'-flanking region (72 bp repeats)

deletion of this region drastically affects transcription

orientation and position independent

bound by enhancer-binding proteins
experiment showing effects of deletion in gamma2b H-chain enhancer (297)
1. made deletions in intron of gene where they suspected the enhancer was
2. transfected plasmacytoma cells with wt gene and the deletion mutant genes.
3. added radioactive aa to label newly made protein, immunoprecipitated and electrophoresed

found that the larger delta 2 mutation had profound effects on transcription
silencers in eukaryotic promoters (298)
cause chromatin to coil up into a condensed, inaccessible form, preventing transcription of neighboring genes
2 types of eukaryotic transcription factors (L5)
1. general TF
2. gene-specific TF
general transcription factors in eukaryotes (L5)
recruit RNA pol (weakly)

provide basal level of transcription
class II TF pre-initiation complex (303)
general TF and RNA pol II

factors: IIA-H

TFs assemble in a specific order
experiment that shows what order eukaryotic class II TFs bind (303)
METHOD: gel mobility shift assay
Performed assays with TFIID, A, B, F, RNA pol II, labeled DNA containing promoter.

shows TFIIF does not bind in absence of pol II (responsible for bringing it to the complex)

Nothing binds if TFIID is absent-->is the first to bind. A is next, then B. E, then H adds to F.
TFIID (305)
complex protein containing TBP and 8-12 TBP-associated factors (TAFs)
TBP (305)
highly conserved

CTD is most important (confirmed by trunctations in which the CTD was enough for transcription to occur)

saddle shaped: lines up with DNA along minor groove and bends TATA box to an 80-degree curve, opening it up.

required by all 3 RNA pols
experiment showing footprinting of DABPolF complex (306)
METHOD: DNase footprinting
DNase footprinting with TFIID, A, B and with TFIID, A, B, F, RNA pol II

when RNA pol and F joined the complex, the footprint was extended to +17, which correlates with large size of RNA pol II.
experiment showing how TBP binds to TATA box (307)
1. Replaced T's with C's and A's with I's, yielding a CICI box instead of a TATA box (C and I look the same as T,A in the minor groove)
2. Bound TBP to CICI box and performed gel mobility shift assays using DNA frags containing: CICI boxes, TATA boxes, or non-specific DNA with no promoter elements.

found that substituting CICI for TATA had little effect on yield. Thus, TBP binds at minor groove of DNA.
2 functions of TAFIIs (309)
1. interaction with the promoter
2. interaction with gene-specific transcription factors
experiment that shows the activity of TBP and TFIID on 4 different promoters (310)
1. tested Drosophila transcription system containing either TBP or TFIID on templates with 4 different promoters. 2 of the promoters had just a TATA box, 2 had a TATA box + Inr + DPE.
2. transcribed in vitro, assayed by primer extension

found TPB and TFIID fostered transcription equally well when just a TATA box was present, but TFIID did much better when the Inr and DPE were present. Thus, the interaction between TBP and other TAFs is important.
experiment to determine which TAFs are bound to Inr, DPE of promoter (311)
1. photo-crosslinked TFIID to 32P-labeled template containing: TFIID found to labeled template (substituted with BrdU); TBP/250/150; TBP alone.
2. Irradiated complexes with UV light to crosslink
3. digested DNA with nuclease and did SDS-PAGE.

TAF250 and 150 became labeled, indicating they were in close contact with the DNA's major groove and bind to the Inr and DPE. TBP was not labeled (binds only to TATA box).

This binding was later confirmed with DNase I footprinting.
coactivators (311)
factors that have no transcription-activation ability of their own, but help other proteins to stimulate transcription (e.g., Sp1 with TAF110 binding to GC boxes).
model for interaction between TBP and TATA-containing or TATA-less promoters (312)
TATA containing promoter: TBP can bind by itself to TATA box and can also bind in company of all other TAFs of TFIID or a subset of them.

TATA-less promoter with Inr + DPE: TBP cannot bind by itself. It can bind with all TAFIIs through interactions with TAF250 and 150. These two are sufficient for TBP binding.

TATA-less promoter with GC boxes: TBP cannot bind by itself. It can bind with all TAFs along with coactivator Sp1. TAF250, 150 and 110 are sufficient to anchor TBP to Sp1 bound to GC boxes.

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