Anti-sigma factors

Anti-sigma factor binds to sigma factor and inhibits its activity.

Sigma factor is an important protein which starts the transcription by binding with RNAP; anti-sigma factor is a protein which inhibits the activities of sigma factor affect by several mechanism, such as add up anti-sigma factor between sigma or twist the anti-sigma factor around sigma.[2]

"In bacteria, the regulation of gene expression is the basis for adaptability, morphogenesis, and cellular differentiation. From all the different regulatory layers, regulation of transcription initiation is a very important step for controlling gene expression."[3]

Each sigma factor has an associated anti-sigma factor which regulates it. These anti-sigma factors are divided into either cytoplasmic or inner membrane bound anti-sigma factors.[4] Cytoplasmic bound anti-sigma factors are made up of FlgM, DnaK, RssB, & HscC.[4] Inner membrane bound anti-sigma factors are made up of FecR & RseA.[4] Anti-sigma factors are simultaneously transcribed with their associated sigma factor.[4][2] This gives rise to a negative feedback loop effect, which takes part in maintaining proper levels of both contrasting factors.[4][2]

Some research studies show that because of their ability to inhibit some cell processes and activate others, Anti-sigma factors can likely play an important role in function rather than being sigma factor destroyers. Researchers have studied several anti-sigma factor activities in the cell such as RsrA (Redox-sensitive), which is a key sensor of thiol–disulphide and a negative regulator ofσR (binds σR and inhibits σR-directed transcription only in vitro), what means that it needs some sensitive conditions to happen. They conclude by using Thioredoxin that it is able to reduce the oxidize RsrA.[5]

There are four steps to start the complex: first, the relative sigma factor appears in a particular environmental signal. Second, different transcriptional factor and sigma factor interact with their correspondent anti-sigma factor. Third, anti-sigma factor has different roles: either stay not active or activate it in specific environmental signal. Finally, since the signals disappear, anti-sigma factor inhibit the sigma factor by confinement.[2]

In prokaryotes, E. coli has seven different sigma factors depends on the environment condition. Each one specific anti-sigma factors,[4] check the below table for details:

As another Anti-sigma factor example is σH which regulate the osmotic stress response and the morphological differentiation in Streptomyces coelicolor as the studies results.[6] From the same study it can be concluded that every anti-sigma factor has a specific gene location to act and affect in the cell.

In E. coli, anti-anti sigma factors allow the regulation of transcription and therefore a differentiated gene expression as response to environmental conditions. Anti-anti sigma factors can thereby function as negative or positive regulatory elements, depending on its classification.[6]

T4 bacteriophage uses anti-sigma factor to ruin the Escherichia coli polymerase in order that direct exclusive transcription of its own genes.

(AsiA is an anti-sigma factor gene that is required for bacteriophage T4 to be developed). Which means that AsiA is an essential anti-sigma factor in bacteriophage.[5][4][7][6]

Sigma B was the first anti-sigma factor identified in a bacterium. It is found in Bacillus subtilis and other similar bacteria. Sigma B is a stress response factor that plays a role in survival and against destruction  that could be caused by other organisms such as mammals. General stress responses that are controlled by Sigma B are stimulated by things like temperature, salt concentration, energy depletion, etc. Once activated, Sigma B binds to the RNAP and recognizes a promoter, causing inhibition of the stimuli. Because Sigma B orthologs are conserved in various gram-positive bacteria, this anti-sigma factor plays an essential role in the evolution of different bacteria and their ability to respond to stressing factors. Scientist have found that the anti- sigma factor, Sigma B controls more than 150 genes that are influential in stress response.[8][9]

When Bacillus subtilis is not under stress conditions, it is negatively regulated by the anti-sigma factor, Rsbw. RsbW is an anti-sigma factor that regulates another anti-sigma factor , sigma B. RsbW binds to sigma B and prevents it from forming an RNA polymerase holoenzyme. However, in stressed conditions, the unphosphorylated form of the protein, RsbV, competes with Sigma B for binding to RsbW. RsbV binds to RsbW, allowing sigma B to bind to the core RNA polymerase, resulting in the expression of stress response.[10][11]