Gene Regulation: Prokaryotes• Introduction• Why gene regulation?• Lac Operon• Structure of the

operon • Operation of the

operon • Positive regulation • Trp Operon

Why gene regulation?

• Constitutive genes • Facultative genes • Jacob & Monod • Example: Lac operon• B-galactosidase

cleaves lactose

Jacob and Monod expt

• Is enzyme made de novo or inactive in cytosol?

Lac Operon:Structure of the operon

• Operon: cluster of genes for a particular function

• Polycistronic • Three structural genes

(B-galactosidase, permease, transacetylase)

• Operator • Promoter

Lac operon

Operation of the operon

• repressor protein • inducer molecule

(allolactose)

Mutations

Mutations

Studies of regulation

• Partial diploids (merozygotes)

• cis and trans factors • Oc mutants • i gene mutants: Is

Studies of regulation

• cis and trans regulation

• Oc mutants

• I- gene mutants

• P- and Is mutants

Positive regulationEffect of glucose and lactose CAP/cAMP regulation Diauxic growth

Trp Operon

• Structural genes (5) • Repressible operon • Co-repressor • Attenuator (unique to

prokaryotes)

Repressible Gene

Attenuator

Attenuator