Σ factor

σ factor (also known as sigma factor) is a protein that is a crucial component of RNA polymerase, the enzyme complex responsible for transcription in bacteria. It is a transcription factor that controls the initiation of transcription.

Function

The primary role of the σ factor is to guide the RNA polymerase to specific promoter sequences on the DNA where transcription should begin. It achieves this by recognizing and binding to the promoter sequences, thereby facilitating the binding of the RNA polymerase.

There are several types of σ factors, each recognizing different sets of promoters, thereby controlling the expression of different groups of genes. This allows the bacteria to respond to different environmental conditions by changing the type of σ factor that is associated with the RNA polymerase.

Types

In Escherichia coli, a model organism for bacteria, seven different σ factors have been identified. The primary σ factor, σ70, is responsible for the transcription of most genes under normal conditions. The other σ factors, known as alternative σ factors, control the transcription of specific groups of genes in response to specific environmental conditions.

Structure

The structure of σ factors varies, but most have four conserved regions known as σ1, σ2, σ3, and σ4. These regions are involved in recognizing and binding to the promoter sequences, and in interacting with the RNA polymerase.

Role in disease

Some pathogenic bacteria use σ factors to control the expression of virulence genes, which are genes that contribute to the ability of the bacteria to cause disease. This makes σ factors potential targets for the development of new antibacterial drugs.

See also

• Transcription (genetics)
• RNA polymerase
• Promoter (genetics)
• Protein
• Transcription factor
• Escherichia coli