Chapter 16 Control of Gene Expression

Topics to discuss DNA binding proteins Prokaryotic gene regulation –Lac operon –Trp operon Eukaryotic gene regulation Today’s lecture

6 groups of DNA-binding regulatory proteins have been identified

Prokaryotic Gene Regulation Nutritional enviroment and a bug’s growth!

Operons Operons provide coordinate expression

A model operon

Now let’s look at 2 groups of operons Negative inducible operons Negative repressible operons

INDUCIBLE Negative inducible operon

Turned on

repressor

Now let’s look at 2 specific operons The Lactose operon The Tryptophan operon

Francois Jacob and Jacques Monod 1961 Studied lactose metabolism in prokayotes J. Monod Won the Nobel Prize in 1965

Sources of prokaryotic energy 1. Disaccharide 2. Monosaccharide Lactose Glucose

Building the lac operon

ZYAOP I Lac Operon and Proposed Arrangement with control I gene Not technically part of the “operon”

Negative inducible operon

Conditions: No glucose but lactose is present

Lactose Metabolism Requires Coordination of all these genes!

Laboratory Exercise: Mutational Analysis of the lac operon

Try out your ability to reason through the questions.

Predict if you expect to obtain the proteins from the lacZ and lacY genes IF certain mutations are present in the operon.

The next three slides are the “key” to the mutations.

Mutational Key: Any + means wildtype. Any – means mutant. Two other mutants: “O c and I s ” I - cells synthesize full levels in the presence or absence of inducer- Transcription Turned ON. Inhibitor cannot bind to DNA P - the DNA promoter mutation : cannot bind RNA polymerase Transcription OFF I s super-suppressors can bind DNA but not inducer. DNA and Transcription Turned OFF. O c is an DNA mutation: repressor cannot bind. Transcription ON.

Examples Allolactose CANNOT BIND DNA binding site I - = DNA binding site mutated, prevents binding, allows transcription I s =the Super-repressor VERSUS

Next: 3 important terms of DNA control. Constitutive activity Trans acting Cis acting

LactoseNo lactoseLactose I+P+O+Z+Y+I+P+O+Z+Y+ - + I-P+O+Z+Y+I-P+O+Z+Y+ I+P-O+Z+Y+I+P-O+Z+Y+ I+P+OcZ+Y+I+P+OcZ+Y+ I + P + O + Z - Y - / I - P + O + Z + Y + I + P + O c Z + Y - / I + P + O + Z - Y + I + P + O c Z - Y + / I - P + O + Z + Y - I S P + O + Z + Y - / I - P + O + Z - Y + I + P - O c Z + Y + / I + P + O + Z - Y - Β-galactosidasePermease No Lactose

Negative inducible operon

Question: what happens when both lactose and glucose are present together in the same cell?

To answer this question you first need to understand this reaction Adenylyl cyclase Cyclic AMP ATP Glucose may inhibit this enzyme catabolite activator protein + (helix-turn-helix)

cAMP and glucose levels are inversely proportional.

The promoter needs to be in an ideal conformation for RNA polymerase.

How CAP and cAMP affects the promoter END of PART I

Trypthophan Operon

5 genes involved in the synthesis of the amino acid trypthophan

Negative repressible operon

2 shapes to the mRNA

attenuation

Eukaryotic Gene Regulation

Do eukaryotes show coordinate gene regulation? Yes, the same response element may be found in related genes.

Changes in Chromatin structure and eukaryotic gene regulation Chromatin Structure –DNase hypersensitivity ( Histone acetylation DNA methylation