Chapter 15; The Jacob-Monod model for gene regulation

pictures of Jacob and Monod ... JacobMonod1965.GIF

 

Regulation of gene activity via the operon

Enzymes may be divided into two categories

Constitutive enzymes are always present

Regulative enzymes may or may not be present

 

 

What controls the regulative enzymes; a problem of turning genes on and off

Answer via mutation analysis

Mutations may be in structural genes (for enzymes) or regulation sequences of DNA

Wild type E. coli will produce the enzyme beta-galactosidase when lactose is present.

Some mutant E. coli will produce beta-galactosidase if lactose is present or absent; they are constitutive mutations

Other mutations are in the beta-galactosidase gene

Two types of mutations.... OperonMutationsFinal.GIF

 

The model:

Location of the lac operon.... OperonMap.GIF

Model of a portion of the E. coli chromosome: operon2.GIF

Concept of the allosteric protein operon3.GIF

Lactose not present....operon4.GIF

Lactose present....operon5.GIF

 

Analysis: Mutations of the lac operon

Overview... OperonMutationsOverview.GIF

Mutation in repressor gene ... repressorminus.GIF

Mutation in repressor gene...repressorS.GIF

Mutation ... OperatorMutation.GIF

 

Genotypes and the operon model (some partial diploids for cis trans analysis)

important: repressor protein may act on all chromosomes - trans acting

important: operator DNA cis acting

Table of some genotypes... OperonGenotypes.html

Examples graphics.... ioz6.GIF... ioz7.GIF ... ioz8.GIF

List of steps.....operonWorkbook2.gif

from workbook: operonWorkBook.gif

 

A tutorial which may help with the complex genotypes OperonHome.html

In gene regulation we have cis vrs trans effects.

for cis acting elements, the effect must be between adjacent segments of DNA

for trans acting proteins, there is some movable object which may influence another chromosome

cis acting elements -   Promoters, operators, enhancers

Trans acting proteins - repressors, proteins attaching to promoters

              Helix turn helix motif... OperonHelixTurnHelix.gif

                and  Zinc finger, leucine zipper motifs

Palindrome DNA

        see restriction sites

        lac operator segment:

                            5' AATTGT................ACAATT 3'

                           3'  TTAACA................TGTTAA 5'

a palindrome web site...http://ot.3w.w3.to/

 

 Map of control region..... OperonMap2.gif

Fit of CAP (catabolite activating protein) to DNA ... (not on web)

A model for repressor-operator....OperonModelScience.GIF

Reference: Lewis, M., et al. 1996 Crystal structure of the lactose operon repressor and its complexes with DNA and inducer. Science 271(5253): 1247-12...

Cover picture..(not on web)