Chapter 16 Control of Gene Expression

Topics to discuss DNA binding proteins Prokaryotic gene regulation Eukaryotic gene regulation

6 groups of DNA-binding regulatory proteins have been identified

Prokaryotic Gene Regulation

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

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”

Lactose Metabolism Requires Coordination of all these genes!

Negative inducible operon

Conditions: No glucose but lactose is present

Lactose Metabolism Requires Coordination of all these genes!

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

Overview of: Mutational Analysis of the lac operon 3-24p. Lab manua

Monod and Jacob Discovery of lac operon control

Try out your ability to reason through the questions. I geneP geneZ,A,Y genes I+I+ P+P+ Z +,A +, Y + I-I- P-P- Z - or A -, or Y - IsIs O O+ Oc

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

Now, back to glucose and the lac operon! Lac

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

Conditions: glucose present and lactose

Need to understand this reaction Adenylyl cyclase Cyclic AMP ATP Glucose may inhibit this enzyme catabolite activator protein +

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

How CAP and cAMP affects the promoter

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 DNase hypersensitivity Histone acetylation DNA methylation

For Your Information Next 4 slides

Experimental tests on the repressor: I + cells synthesize full levels of the lac enzymes only in the presence of an inducer I - mutations NO DNA BINDING ACTIVITY, TRANSCRIPTION OCCURS EVEN IN ABSENCE OF INDUCER! I s mutation NO LACTOSE BINDING ACTIVITY but has DNA BINDING ACTIVITY. NO TRANSCRIPTION EVEN WITH INDUCER! Oc mutation: constitutive activity

Trans (across) acting product

Oc= constitutive operator, notice how it affects transcription.

Mutations to inducer binding domain of repressor

Extra slides

Table I.

Table 2.

Table 3.

Allosteric affect of DNA binding protein

The Lac promoter and its role in lac transcription

Repressor has two binding sites. Lactose binding site DNA Operator binding site

ITPG: Binds repressor but is not cleaved.