Week 9 - Prokaryote Gene Regulation

Operon

Cluster of genes controlled by single promoter + regulatory elements

Regulatory Elements - 3

Promoter

Operator - regulatory proteins bind

Regulatory gene - separate gene code for regulatory protein

Lac Operon - Classification

Inducible

Lac Operon - Order

CAP

P

lacI

lacP

lacO

lacZ

lacY

lacA

CAP

Catabolite activator protein

lacI

Regulator

lacY - Code for

Lactose permease

Lactose Permease

Transmembrane protein pump lactose into cell

lacA - Code for

Transacetylase

No Lactose

lacI - repressor protein

Bind to operator

RNA pol bind to promoter

Stop

No enzymes produced

Lactose Present

Allolactose bind to repressor

Allosteric shift

Doesnt bind to operator

RNA pol bind to promoter

Transcription

Enzymes produced

Allosteric Shift

Molecule binds to 1 site on protein & cause change at separate site on same protein

Lactose + Low Glucose

High cAMP

cAMP + CAP complex

CAP bind to CAP site

RNA pol strongly bind

High transcription

Lactose + High Glucose

Low cAMP

No complex

RNA weakly bind

Low transcription

Tryptophan Operon - Classification

Repressible

Low Trp = ON

Repressor doent bind to operator

RNA pol bind to promoter

Transcription

High Trp = OFF

Trp bind to repressor protein

Allosteric shift

Cant bind to operator

No transcription

Attenuation

Fine tuning

Leader Seqeunce

Start of trp mRNA + code for leader peptide

Attenuation - Process

Ribosome sensor - detect trp levels during translation of leader peptide

High trp - RNA pol detach + premature termination

Low trp - continue