The MicA RNA (also known as SraD) is a small
non-coding RNA that was discovered in ''
E. coli
''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus ''Escher ...
'' during a large scale screen. Expression of SraD is highly abundant in
stationary phase, but low levels could be detected in
exponentially growing cells as well.
Function
This RNA binds the
Hfq protein and regulates levels of
gene expression
Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product that enables it to produce end products, protein or non-coding RNA, and ultimately affect a phenotype, as the final effect. The ...
by an
antisense mechanism. It is known to target the OmpA gene in ''E. coli'' and occludes the ribosome binding site.
Under conditions of envelope stress, micA transcription is induced. MicA,
RybB RNA
RybB is a small non-coding RNA was identified in a large scale screen of ''Escherichia coli''. The function of this short RNA has been studied using a transcriptomic approach and kinetic analyses of target mRNA decay ''in vivo''. RybB was identifi ...
and
MicL RNA transcription is under the control of the
sigma factor
A sigma factor (σ factor or specificity factor) is a protein needed for initiation of transcription in bacteria. It is a bacterial transcription initiation factor that enables specific binding of RNA polymerase (RNAP) to gene promoters. It is ho ...
sigma(E).
In ''E.coli'', SraD also interacts in ''cis'' and ''trans'' with the mRNA species, ''luxS'', ''ompA a''nd ''phoP'', respectively. This observation describes MicA to be the first known sRNA to carry out antisense regulation in both structural configurations. MicA is known to interact with the mRNA encoding the quorum sensing synthase homolog, LuxS in E.coli and both RNAs are processed by the double stranded RNA endonuclease, RNase III. Based on its conservation, this is presumably the case in close relatives and may serve as a long elusive link between envelope stress and quorum sensing.
The PhoPQ
two-component system
In the field of molecular biology, a two-component regulatory system serves as a basic stimulus-response coupling mechanism to allow organisms to sense and respond to changes in many different environmental conditions. Two-component systems t ...
is repressed by MicA.
The RNA presumably pairs with the
ribosomal binding site of phoP mRNA, thereby inhibiting translation.
This links micA to cellular processes such as
Mg(2+) transport,
virulence
Virulence is a pathogen's or microorganism's ability to cause damage to a host.
In most, especially in animal systems, virulence refers to the degree of damage caused by a microbe to its host. The pathogenicity of an organism—its ability to ca ...
,
LPS modifications and resistance to antimicrobial peptides.
In ''S. typhimurium'' MicA has been shown to be involved in
biofilm
A biofilm comprises any syntrophic consortium of microorganisms in which cells stick to each other and often also to a surface. These adherent cells become embedded within a slimy extracellular matrix that is composed of extracellular ...
formation. It is observed that the ''luxS'' mutant biofilm formation process is found to be dependent on MicA in cases where the gene's coding region is deleted, however, it is still not known to what extent MicA is involved in this mechanism.
Site directed mutagenesis has been used to construct mutated forms of MicA forms in order to investigate the RNA determinants important to its stability and function.
Each 'domain' investigated ( 5′linear domain, the structured region with two stem-loops, the A/U-rich sequence and the 3′ poly(U) tail) was altered without affecting the overall secondary structure of MicA however, each 'domain' was found to have a different impact on stability and the ability of MicA to regulate its multiple targets.
References
Further reading
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External links
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Non-coding RNA
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