The ''asd'' RNA motif is a conserved

RNA Ribonucleic acid (RNA) is a polymeric molecule essential in various biological roles in coding, decoding, regulation and expression of genes. RNA and deoxyribonucleic acid ( DNA) are nucleic acids. Along with lipids, proteins, and carbohydra ...

structure found in certain

lactic acid bacteria Lactobacillales are an order of gram-positive, low-GC, acid-tolerant, generally nonsporulating, nonrespiring, either rod-shaped ( bacilli) or spherical ( cocci) bacteria that share common metabolic and physiological characteristics. These bact ...

. The ''asd'' motif was detected by

bioinformatics Bioinformatics () is an interdisciplinary field that develops methods and software tools for understanding biological data, in particular when the data sets are large and complex. As an interdisciplinary field of science, bioinformatics combin ...

and an individual ''asd'' RNA in ''

Streptococcus pyogenes ''Streptococcus pyogenes'' is a species of Gram-positive, aerotolerant bacteria in the genus '' Streptococcus''. These bacteria are extracellular, and made up of non-motile and non-sporing cocci (round cells) that tend to link in chains. They ...

'' was detected by

microarray A microarray is a multiplex lab-on-a-chip. Its purpose is to simultaneously detect the expression of thousands of genes from a sample (e.g. from a tissue). It is a two-dimensional array on a solid substrate—usually a glass slide or silic ...

and

northern hybridization The northern blot, or RNA blot,Gilbert, S. F. (2000) Developmental Biology, 6th Ed. Sunderland MA, Sinauer Associates. is a technique used in molecular biology research to study gene expression by detection of RNA (or isolated mRNA) in a sample.Ke ...

experiments as a 170-nucleotide molecule called "SR914400". The

transcription start site Transcription is the process of copying a segment of DNA into RNA. The segments of DNA transcribed into RNA molecules that can encode proteins are said to produce messenger RNA (mRNA). Other segments of DNA are copied into RNA molecules calle ...

determined for SR914400 corresponds to the 5′-end of the molecule shown in the consensus diagram. Some ''asd'' RNA are associated with genes, such as ''asd'', that are suggestive of a cis-regulatory function. However, several lines of evidence suggest that this is not the biological role of ''asd'' RNAs. First, in some cases, the ''asd'' RNA is not in the

5' untranslated region The 5′ untranslated region (also known as 5′ UTR, leader sequence, transcript leader, or leader RNA) is the region of a messenger RNA (mRNA) that is directly upstream from the initiation codon. This region is important for the regulation of t ...

of any annotated

gene In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...

. Second, in ''

Streptococcus mutans ''Streptococcus mutans'' is a facultatively anaerobic, gram-positive coccus (round bacterium) commonly found in the human oral cavity and is a significant contributor to tooth decay. It is part of the "streptococci" (plural, non-italic lowercase ...

'', there is a strong promoter immediately downstream of the transcription terminator that follows the ''asd'' RNA, and this promoter precedes the downstream gene. This arrangement suggests that ''asd'' RNA transcription is terminated, and the gene is transcribed from the downstream promoter. Finally, although the ''asd'' gene encodes an enzyme,

aspartate-semialdehyde dehydrogenase In enzymology, an aspartate-semialdehyde dehydrogenase () is an enzyme that is very important in the biosynthesis of amino acids in prokaryotes, fungi, and some higher plants. It forms an early branch point in the metabolic pathway forming lysine, ...

, that participates in the synthesis of methionine,

lysine Lysine (symbol Lys or K) is an α-amino acid that is a precursor to many proteins. It contains an α-amino group (which is in the protonated form under biological conditions), an α-carboxylic acid group (which is in the deprotonated &minu ...

and

threonine Threonine (symbol Thr or T) is an amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated −NH form under biological conditions), a carboxyl group (which is in the deprotonated −COO ...

, transcription levels of the ''asd'' gene remain constant even when the concentrations of these amino acids are varied. The sRNA was shown to interact with the

5'UTR The 5′ untranslated region (also known as 5′ UTR, leader sequence, transcript leader, or leader RNA) is the region of a messenger RNA (mRNA) that is directly upstream from the initiation codon. This region is important for the regulation of ...

of the ''mga'' transcript (the multiple virulence gene regulator gene) and was renamed MarS for mag-activating regulatory sRNA. In MarS deletion strains expression of ''mga'' and several Mga-activated genes is reduced. This down-regulation of virulence factors leads to increased susceptibility of the deletion strain to

phagocytosis Phagocytosis () is the process by which a cell uses its plasma membrane to engulf a large particle (≥ 0.5 μm), giving rise to an internal compartment called the phagosome. It is one type of endocytosis. A cell that performs phagocytosis i ...

, reduced adherence to human

keratinocytes Keratinocytes are the primary type of cell found in the epidermis, the outermost layer of the skin. In humans, they constitute 90% of epidermal skin cells. Basal cells in the basal layer (''stratum basale'') of the skin are sometimes referre ...

. However, the lack of MarS increased bacterial dissemination and tolerance towards oxidative stress.

References

External links

* Non-coding RNA {{molecular-cell-biology-stub