Bacterial Transcription Mechanism

Study Notes

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

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

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

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

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

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.