The Genetics of Beta-galactosidase--Encoded by the lacZ gene in E. coli--Laboratory Exercises to Illustrate Gene Regulation

 

Tested Studies in Laboratory Teaching, 2007, Volume 28

Kristene Henne & Sue Karcher

Abstract

Beta-galactosidase is an enzyme that splits lactose into glucose and galactose; it is encoded by the lacZ gene in the lac operon of the bacterium Escherichia coli. An operon is a set of structural genes transcribed as a single messenger RNA and adjacent regulatory regions that control the expression of these genes. Because beta-galactosidase is a relatively stable enzyme that is easily assayable using the substrate ONPG (o-nitrophenyl-beta-galactopyranoside), it is used in laboratory exercises. The beta-galactosidase system of E. coli was studied by scientists François Jacob and Jacques Monod. From their analysis of mutations within the lac operon, they developed a model of transcriptional regulation of the lac operon by the lac repressor. They formulated a model of genetic regulatory mechanisms, showing how, on a molecular level,certain genes are activated and repressed. They received a Nobel Prize in 1965 for this work. This workshop describes a laboratory exercise using E.coli strains with different mutations in the lac operon to demonstrate to students the regulation of beta-galactosidase production in E. coli. Students identify the nature of the mutations in each strain based on their determination of the beta-galactosidase activity of each strain. This laboratory enhances the students' understanding of gene regulation. In addition, we will focus on the historical background and practical applications of the lac operon.

Keywords:  beta galactosidase, Lac operon, lactose-operon inducer, gene regulation, lac repressor

Purdue University (2006)