DNA-binding protein H-NS
| DNA-binding protein H-NS ( Escherichia coli K12) |
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|---|---|---|
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| An H-NS oligomer forms a DNA-H-NS-DNA bridge with the DNA and represses the gene. The RNA polymerase either cannot bind or is locked in the loop, the gene is inactive. | ||
| Mass / length primary structure | 136 amino acids | |
| Secondary to quaternary structure | Homodimer | |
| Identifier | ||
| Gene name (s) | hns (EcoGene) | |
| External IDs | ||
| Occurrence | ||
| Parent taxon |
Enterobacteriaceae , Haemophilus influenzae , Rhodobacter capsulatus |
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The nucleoid-associated protein H-NS (engl. H iStone-like N ucleoid S tructuring protein) is an important Genregulatorprotein in enterobacteria , with mostly reprimierender effect. It plays a key role in adapting to changing environmental conditions and stress. In addition, H-NS protects the bacterium from foreign, potentially harmful DNA. In E. coli there are 200-300 genes under his control and with around 20,000 molecules per cell, it is one of the most common DNA-binding proteins.
Repressive effect
Although H-NS does not bind specifically to DNA for a DNA-binding protein , it can suppress the expression of certain genes very specifically ( silencing ). To this end, it oligomerizes and preferably binds only weakly specifically to AT-rich DNA sequences. If these AT-rich sequences are in the vicinity of a promoter , the RNA polymerase can not start the transcription and the gene is out. Often, H-NS molecules bind both upstream and downstream of the promoter, so that a DNA-H-NS-DNA bridge is created (see graphic) in whose loop the RNA polymerase is “trapped”. If this is the case, the gene is also repressed.
Although H-NS does not bind specifically to AT-rich sequences, it is still able to specifically control genes. This fact can be explained by the fact that many different, highly specific proteins play a role in the activation of the genes that are repressed by H-NS, which can displace H-NS through various mechanisms. Therefore, the activation of the gene repressed by H-NS is called de-repression or anti-silencing.
Protective function
Another central function of H-NS is the repression of foreign DNA absorbed by horizontal gene transfer (xenogeneic silencing). This function protects the bacterium from the harmful effects of phages , which inject their DNA into the bacterium as host cells, which sooner or later perish. As a rule, the recognition takes place through the increased AT / GC ratio of the foreign DNA.
literature
- ↑ Search result UniProt H-NS family
- ↑ Tinka Wolf, Karin Schnetz: Gene regulation in E. coli control by the nucleoid-associated protein H-NS; published in BIOspektrum 2007