Sigma factor

Definition

A sigma factor is a protein that binds to RNA polymerase in prokaryotic cells, guiding it to specific promoter regions of DNA to initiate transcription. By recognizing and attaching to specific sequences in the promoter, sigma factors play a crucial role in the regulation of gene expression, allowing the organism to respond to various environmental conditions by turning genes on or off as needed.

5 Must Know Facts For Your Next Test

1. Sigma factors are essential for the initiation of transcription in prokaryotes, as they help RNA polymerase recognize and bind to promoters.
2. Different sigma factors can direct RNA polymerase to different sets of genes, allowing bacteria to adapt their gene expression based on environmental changes.
3. In E. coli, the primary sigma factor is σ70, which recognizes consensus sequences in promoters for most housekeeping genes.
4. Alternative sigma factors can be activated under specific stress conditions, enabling the expression of genes needed for survival in adverse environments.
5. The binding of a sigma factor to RNA polymerase is a reversible process, meaning that once transcription has started, the sigma factor can be released.

Review Questions

• How does a sigma factor influence the specificity of transcription in prokaryotic cells?
  • A sigma factor influences the specificity of transcription by directing RNA polymerase to specific promoter regions on the DNA. By binding to distinct promoter sequences, different sigma factors enable RNA polymerase to initiate transcription of particular genes. This selective recognition allows prokaryotic cells to fine-tune their gene expression in response to varying environmental conditions and cellular needs.
• Discuss how alternative sigma factors contribute to gene regulation during environmental stress in prokaryotes.
  • Alternative sigma factors provide a mechanism for prokaryotes to regulate gene expression in response to environmental stress. When conditions change, such as heat shock or nutrient deprivation, specific alternative sigma factors are activated. These factors can then guide RNA polymerase to different sets of promoters, leading to the transcription of genes that help the organism survive under stress, thereby allowing for rapid adaptation.
• Evaluate the role of sigma factors in bacterial adaptability and survival in diverse environments.
  • Sigma factors play a pivotal role in bacterial adaptability and survival by facilitating precise regulation of gene expression. They enable bacteria to quickly respond to environmental changes by controlling which genes are transcribed at any given time. This ability to activate or repress gene expression based on external stimuli is crucial for survival in diverse environments, allowing bacteria to optimize metabolic pathways, resist stress, and compete effectively with other organisms.

Related terms

RNA polymerase:

An enzyme responsible for synthesizing RNA from a DNA template during transcription.

promoter:

A specific DNA sequence located upstream of a gene that serves as a binding site for RNA polymerase and sigma factors to initiate transcription.

transcription factors:

Proteins that help regulate the transcription of specific genes by assisting or inhibiting the binding of RNA polymerase to DNA.