In a screen of the ''

Bacillus subtilis ''Bacillus subtilis'', known also as the hay bacillus or grass bacillus, is a Gram-positive, catalase-positive bacterium, found in soil and the gastrointestinal tract of ruminants, humans and marine sponges. As a member of the genus ''Bacillu ...

'' genome for genes encoding

ncRNA A non-coding RNA (ncRNA) is a functional RNA molecule that is not translated into a protein. The DNA sequence from which a functional non-coding RNA is transcribed is often called an RNA gene. Abundant and functionally important types of non-c ...

s, Saito et al. focused on 123 intergenic regions (IGRs) over 500

base pair A base pair (bp) is a fundamental unit of double-stranded nucleic acids consisting of two nucleobases bound to each other by hydrogen bonds. They form the building blocks of the DNA double helix and contribute to the folded structure of both DNA ...

s in length, the authors analyzed expression from these regions. Seven IGRs termed bsrC, bsrD, bsrE, bsrF, bsrG, bsrH and bsrI expressed RNAs smaller than 380 nt. All the small RNAs except BsrD

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 ...

were expressed in transformed ''

Escherichia 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 ...

'' cells harboring a

plasmid A plasmid is a small, extrachromosomal DNA molecule within a cell that is physically separated from chromosomal DNA and can replicate independently. They are most commonly found as small circular, double-stranded DNA molecules in bacteria; how ...

with PCR-amplified IGRs of ''B. subtilis'', indicating that their own promoters independently express small RNAs. Under non-stressed condition, depletion of the

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 ba ...

s for the small RNAs did not affect growth. Although their functions are unknown,

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 ...

profiles at several time points showed that most of the genes except for bsrD were expressed during the vegetative phase (4–6 h), but undetectable during the stationary phase (8 h). Mapping the 5' ends of the 6 small RNAs revealed that the genes for BsrE, BsrF, BsrG, BsrH, and BsrI RNAs are preceded by a recognition site for RNA polymerase sigma factor σ^A.

Type I Toxin/Antitoxin system

It was shown that ''bsrE'', ''bsrG'' and ''bsrH'' pair through intermolecular interactions with newly identified antisense sRNAs. It was suggested that they form type I toxin/antitoxin system that includes an mRNA encoding for a short, toxic peptide (''bsrE'', ''bsrG'' and ''bsrH'' ) and an antitoxin that consists of an antisense RNA. Further studies established that the 294-nucleotide ''bsrG'' encodes a 39-amino-acid toxin, and the 180 nucleotide antisense sRNA called SR4 acts as the antitoxin (they overlap by 123 nucleotides). SR4 interaction with the 3'UTR of ''bsrG'' RNA promotes ''bsrG'' degradation and inhibits its translation. BsrG interferes with cell envelope biosynthesis, causes membrane invaginations and delocalisation of the cell wall synthesis and initiates autolysis. The 256 nucleotide ''bsrE'' RNA encodes 30 amino-acid toxin peptide. Its antitoxin gene, SR5 overlaps by 112 nucleotides at the 3' end of bsrE. The antitoxin SR5 promotes bsrE degradation but unlike SR4 it does not directly inhibits toxin mRNA translation.

References

{{reflist RNA Molecular genetics

Type I Toxin/Antitoxin system

See also

References