Lecture 19: Metabolic Regulation II

Applying Lessons of Lac Operon

microbes have to respond to a changing environment quickly

- they have to compete for their niche or move to another one

- must sense the environment; ex lac operon responds to change in fuel source

- lac operon is inducible

Arginine Operon

repressible operon

- normally expressed but can be turned off/on

- if arginine is present, it acts as a corepressor and physically blocks RNA polymerase from synthesizing genes for arginine biosynthesis

Sensing the Environment

two-component signal transduction

- sensor kinase and response regulator

Sensor Kinase

binds to environmental change on the outside of the cell

- causes change on the intracellular side of the cell

- activates itself via phosphorylation

Response Regulator

transcription factor; binds to DNA

- activated via phosphorylation by sensor kinase

- mediates expression by altering transcription; negative/positive

EnvZ-OmpR System

two component system that senses osmotic changes to maintain homeostasis

- sensor histidine kinase autophosphorylates and activates the OmpR response regulator

- when activated, it activates the transcription of ompC and activates ompF in low osmolarity and represses it at high osmolarity

Sigma Factors

regulate transcription of all genes

- s^70 initiates transcription at most genes

- alternative s factors are used for different cases

- controlled by altered transcription and translation

Heat Shock Response of E. coli

regulated by s32 at 30C

- sigma factor is transcribed and stays in cytoplasm by hairpins; where binding site is located

- when microbe is at an increased temperature hairpins melt; ending up as a single stranded RNA and ribosome binding site is available

- allows for translation of sigma factor and regulates the heat shock genes

Anti-Sigma Factors

inhibit sigma factors by binding specific sigma factors and blocking its access from binding to DNA

- release of sigma factors from their anti-sigma factor is important for flagella construction

Secondary Messengers

don’t serve as biosynthetic precursors but have regulatory

function

- they alter activities and regulate proteins and responses inside the cell

- ex. cAMP

Stringent Response

stress response that allows them to adapt to nutrient depravation

- decrease rRNA transcripts made for ribosome assembly

Biofilms

community of microbes

- multi-species communities attached to a surface

- as attachment increases, it attracts other microbes

- anaerobic microbes: grow in the center

- aerobic microbes: grow toward the outside

- ex. cavities, gum disease, ponds, implants, catheter

Quorum Sensing

communication between microbes in biofilms