Bacterial Transcription Mechanism

Transcription in Bacteria

RNA Polymerase

• The primary enzyme responsible for transcribing DNA into RNA in bacteria
• Consists of 5 subunits: α2, β, β', ω, and σ (sigma factor)
• The σ subunit is responsible for recognizing and binding to specific DNA sequences
• The core enzyme (α2, β, β', ω) is responsible for the transcription process

Sigma Factors

• A family of proteins that bind to the RNA polymerase core enzyme, allowing it to recognize and bind to specific DNA sequences
• Different sigma factors recognize different promoter sequences, allowing for the regulation of gene expression
• The most common sigma factor in E. coli is σ70 (RpoD)
• Sigma factors can be classified into two groups:
  • Primary sigma factors: essential for transcription and recognition of housekeeping genes
  • Alternative sigma factors: regulate transcription of specific genes in response to environmental stimuli

Transcriptional Termination

• The process by which transcription is stopped and the RNA polymerase is released from the DNA template
• There are two main mechanisms of transcriptional termination in bacteria:
  • Intrinsic termination: uses a terminator sequence that forms a hairpin loop, causing the RNA polymerase to pause and release the transcript
  • Rho-dependent termination: uses the Rho protein to bind to the transcript and pull it away from the RNA polymerase, causing termination
• Transcriptional termination is an important mechanism for regulating gene expression and preventing the transcription of unwanted genes

Transcription in Bacteria

RNA Polymerase

• Primary enzyme responsible for transcribing DNA into RNA in bacteria
• Comprised of 5 subunits: α2, β, β', ω, and σ (sigma factor)
• σ subunit recognizes and binds to specific DNA sequences
• Core enzyme (α2, β, β', ω) carries out the transcription process

Sigma Factors

• Family of proteins that bind to RNA polymerase core enzyme, enabling recognition of specific DNA sequences
• Different sigma factors recognize distinct promoter sequences, regulating gene expression
• σ70 (RpoD) is the most common sigma factor in E. coli
• Classified into two groups:
  • Primary sigma factors: essential for transcription and recognition of housekeeping genes
  • Alternative sigma factors: regulate transcription of specific genes in response to environmental stimuli

Transcriptional Termination

• Process by which transcription is stopped and RNA polymerase is released from DNA template
• Two main mechanisms:
  • Intrinsic termination: uses terminator sequence that forms a hairpin loop, causing RNA polymerase to pause and release transcript
  • Rho-dependent termination: uses Rho protein to bind to transcript, pulling it away from RNA polymerase, causing termination
• Transcriptional termination crucial for regulating gene expression and preventing transcription of unwanted genes

Mutation Types

Insertion Mutation

• An insertion mutation occurs when one or more nucleotides are added to a DNA sequence.
• This type of mutation can alter the reading frame of the genetic code, resulting in a non-functional or abnormal protein.
• The consequences of an insertion mutation include:
  • Frameshift mutation, where the reading frame is shifted, leading to a completely different amino acid sequence.
  • Premature stop codon, where the insertion introduces a premature stop codon, resulting in a truncated protein.
  • Altered gene expression, where the insertion affects the regulation of gene expression, leading to changes in protein production.
• Examples of insertion mutations include:
  • Sickle cell anemia, where a single nucleotide insertion in the HBB gene leads to a frameshift mutation, resulting in abnormal hemoglobin production.
  • Cystic fibrosis, where a three-nucleotide insertion in the CFTR gene leads to a premature stop codon, resulting in a non-functional protein.