Abstract
Non-coding small RNAs (sRNAs) have been identified in the wide range of bacteria (also pathogenic species) and found to play an important role in the regulation of many processes, including toxin gene expression. The best characterized prokaryotic sRNAs regulate gene expression by base pairing with mRNA targets and fall into two broad classes: cis-encoded sRNAs (also called antisense RNA) and trans-acting sRNAs. Molecules from the second class are frequently considered as the most related to eukaryotic microRNAs. Interestingly, typical microRNA-size RNA molecules have also been reported in prokaryotic cells, although they have received little attention up to now. In this work we have collected information about all three types of small prokaryotic RNAs in the context of the regulation of toxin gene expression.
Highlights
The first hypothesis about the regulatory role of RNA molecules on the level of gene expression appeared in 1961 and was proposed by two outstanding scientists Francois Jacob and JacquesMonod [1]
For transparency and clarity of the data presented in particular sections, we review separately small phage and bacterial RNAs (sRNAs) originating from the bacterial chromosome and molecules encoded within horizontally acquired genetic elements, with a particular focus on phage encoded sRNAs
In the light of the current knowledge that the presence of a longer hairpin precursor is crucial for the final processing of eukaryotic microRNAs [52], we suggest that at least seven molecules discussed here might be considered as microRNA type molecules [20,22]
Summary
Another small RNA, encoded by a prophage present in the genome of EHEC bacteria, has been identified by Sudo and collaborators [42] This molecule is called Esr, and was detected as an approximately 70-nucleotide long transcript with a predicted Rho-independent terminator and Hfq-interacting structure. Acting in trans IsrK sRNA has been identified within the Gifsy-1 prophage of Salmonella bacteria This molecule acts as small RNA to control the production of the toxic AntQ protein, playing a significant role in bacterial growth arrest and cell death [14]. An additional non-coding intragenic RNA molecule of unknown function has been identified within the genome of the φR1-37 bacteriophage infecting some strains of Yersinia enterocolitica [31] Molecules selected from these two phages are the first examples of characterized small trans-acting RNAs encoded by virulent phages. Potential targets for these molecules have been found on the genomes of phage hosts which are human pathogens able to release dangerous toxins, the functions of the identified molecules are not yet understood
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