Microbial Genetics (Micr340)

Lecture 15Regulation of Gene Expression

Types of regulation

Transcriptional regulation (most common) occurs through proteins called transcriptional regulators Negative regulation: a mutation that inactivates

the regulatory gene will allow transcription of an operon, even in the absence of inducer

Positive regulation: a mutation that inactivates the regulatory gene will prevent transcription, even in the presence of inducer

Post transcriptional regulation Translational regulation

Negative regulation

lac operon example

Operators for lac operon

Control region for lac operon

Negative regulation

gal operon example

Effect of additional copies of operator regions

Tryptophan biosynthetic operon

Negative Regulation of Tryptophan (trp) operon

Positive regulation

L-ara operon example

AraC:A positive regulator& an antiactivator

Maltose operons

Regulation by attenuation of transcription

Attenuation in trp operon

Attenuation in trp operon (continued)

Attenuation in trp operon (continued)