MCB3025F: Transcription Regulation in Prokaryotes - Detailed Study Notes

MCB3025F: Transcription Regulation in Prokaryotes

Course Details

  • Instructor: Dr. Felix S Dube

  • Department: Molecular and Cell Biology & Institute of Infectious Disease and Molecular Medicine

  • University: University of Cape Town

  • Email: sizwe.dube@uct.ac.za

  • Lab Location: Lab 227

Module Aim & Learning Outcomes

  • Aim: To develop a mechanistic, quantitative, and systems-level understanding of how prokaryotic cells regulate transcription in response to environmental, metabolic, and evolutionary pressures.

Learning Outcomes

By the end of the module, students should be able to:

  • Mechanistically explain transcription initiation regulation at bacterial promoters under different physiological states.

  • Compare and evaluate different regulatory strategies, such as:

    • Local control vs. global control.

    • Repression vs. activation.

    • Transcriptional control vs. post-transcriptional control.

  • Interpret experimental data from:

    • Transcriptional reporter assays.

    • RNA-seq (RNA sequencing).

    • ChIP-seq (Chromatin Immunoprecipitation followed by sequencing).

    • Mutational studies.

  • Predict regulatory outcomes when environmental variables (e.g., nutrients, stress, antibiotics) change in pneumococcus.

  • Explain how transcription regulation shapes evolution, virulence, and antibiotic resistance.

Integration Across Diverse Physiological States

Physiological State Overview

  • Rapid growth:

    • Dominant Mechanism: σ⁷⁰ dominance; strong rRNA promoters.

    • Transcriptional Outcome: Biomass production.

  • Nutrient limitation:

    • Mechanism: (p)ppGpp accumulation.

    • Outcome: Reduced ribosomal genes.

  • Stress:

    • Mechanism: Alternative sigma factors.

    • Outcome: Stress regulon activation.

  • High cell density:

    • Mechanism: Quorum sensing.

    • Outcome: Coordinated population response.

  • Antibiotic exposure:

    • Mechanism: Stress signaling and competence activation.

    • Outcome: Adaptive gene uptake.

Importance of Studying Microbial Communities

  • Microbial communities play significant roles in:

    • Immune function.

    • Inflammatory responses.

    • Metabolic functions.

Host-Pathogen-Microbiome Disease Paradigm

  • Emphasis on the interactions between pathogens, microbiomes, and host responses to disease.

  • Courtesy of: Claire Fraser.

Challenges in Antimicrobial Resistance

Superbugs and the Antibiotic Bottleneck

  • Key Points:

    • Rise in antibiotic-resistant bacteria (e.g., Penicillin R, Methicillin R, Vancomycin R).

    • Highlighted antibiotics associated with resistance:

    • Penicillins, Methicillin, Cephalosporins, Vancomycin, Tetracycline, Gentamicin, etc.

    • Notable timeline from 1890 to projected 2030, marking innovation gaps in antibiotic development.

Prokaryotic Transcription Initiation

Overview

  • Primary Control Point: Transcription initiation is crucial for regulating gene expression in bacteria.

Key Stages in Transcription Initiation

  1. Initiation (RNAP Recruitment):

    • Sigma factor (σ) recognizes and binds to the promoter, specifically the “TATA” box.

    • This binding signals RNA polymerase to attach and form a holoenzyme.

    • Different σ classes regulate gene expression differently.

    • The weak double bonds in the TATA box allow for the formation of an open complex.

  2. Elongation/Polymerization:

    • The template DNA strand is used to synthesize complementary mRNA.

    • Ribonucleotides are added at the 3’ end of RNA via phosphodiester bonds.

    • The transcription bubble moves at approximately 50 nucleotides per second, producing a growing mRNA strand that reads 5’ to 3’.

  3. Termination:

    • Transcription stops at a designated termination signal where mRNA and the transcription bubble are released.

    • In contrast to prokaryotes, eukaryotes undergo three post-transcription modifications:

      • RNA capping (methylation).

      • Polyadenylation.

      • Splicing of introns, leaving exons.

Promoter Architecture as a Regulatory Determinant

Definition and Function

  • Promoter:

    • Recognition and binding site for RNA polymerase, orienting it for transcription initiation.

    • A blocked promoter prevents gene transcription.

    • Operators may be associated with promoters.

    • Composed of two consensus sequences located -35 and -10 nucleotides upstream of the transcription start point (+1).

    • The -10 sequence is also called the Pribnow box or TATA box.

Promoter Efficiency

  • Types of Promoters:

    • Strong promoters typically have unaltered consensus sequences, resulting in efficient transcription.

    • Weak promoters have substitutions in this region, affecting their efficiency.