Regulation of transcription

Promoter

determines where transcription begins / binding site for RNA Pol

operator

adjacent to or overlapping promoter

binding site for repressor proteins

activator/inducer

binding site for activator protein

Regulation in prok

Positive control: requires an activator protein to bind to the activator to start

Negative control: transcription is blocked by a repressor protein at the operator site (default setting) → without the repressor, RNA Pol proceeds

effector molecules

act as an inducer:

1. bind to the activator protein

2. bind to repressor at operator and remove it from the system

What is the ground state of a prok gene?

ON (=transcribed)

operon

a linear sequence of genes that is regulated as a group

co-ordinate control: if one gene is transcribed, all are transcribed

Lac operon

sugar metabolism in E coli

glucose is preferred

high glucose no lactose:

1. repress transcription of alt sugar

2. low cAMP → CAP cannot bind to activator

3. no lactose = lac repressor protein binds

=> Lac Operon is OFF

high glucose high lactose:

1. low cAMP => CAP cannot bind to activator

2. yes lactose = lac repressor cannot bind

=> Lac Operon is ON - low productivity bc no CAP binding

no glucose

1. high cAMP = CAP binds

2. yes lactose: lac repressor cannot bind

=> Lac Operon is ON

LAC OPERON IS ONLY ON WHEN LACTOSE IS PRESENT TO REMoVE LAC REPRESSOR

polycistronic

one mRNA codes for multiple proteins and are translated simultaneously (multiple Shine-dagarno sequences in 1 mRNA)

cAMP

effector molecule - cyclic adenosine monophosphate

signaling molecule - signals low glucose level

bind to the allosteric site of the inducer protein CAP → activate CAP and allows it to bind the activator site of Lac Operon

→ turn on transcription

CAP = catalyzed activator protein

what is the ground state of most euk gene?

OFF

is there operons in euk

NO

Which molecule must be present for activation of transcription?

RNA Pol 2

Heterochromatin

condensed chromatin - tightly packed nucleosomes

prevents transcription

DNA modification (methylation): shut down expression long-term

deacetylation +methylation: stabilize condensed structure

epigenetic modifications

Euchromatin

open chromatin w spaced histones

active transcription

acetylation opens DNA structure and allow histones to be moved

DNA modification: NOT methylated

other regulatory proteins and RNA Pol 2 bind to euchromatin to activate transcription

enhanceosome

a complex that activates transcription

promoter region in euk

basal promoter (required for ANY transcription):

+1 transcription start and -30 TATA box

proximal promoter (close by):

contains transcription factor binding sites

extends very far upstream from basal promoter

contains ending sites for both activators and repressors

distal regulatory regions (far):

function as silencers or enhancers

far away from the TSS

can be found in introns

cell-specific expression

transcription factors

interact w DNA and other protein to regulate gene expression

unique combination of TF determine the gene being transcribed

can activate transcription: bend DNA to allow more TF to bind

or repress transcription