Abstract
Bacterial genomic islands are often flanked by tRNA genes, which act as sites for the integration of foreign DNA into the host chromosome. For example, Bacillus cereus ATCC14579 contains a pathogenicity island flanked by a predicted pseudo-tRNA, tRNAOther, which does not function in translation. Deletion of tRNAOther led to significant changes in cell wall morphology and antibiotic resistance and was accompanied by changes in the expression of numerous genes involved in oxidative stress responses, several of which contain significant complementarities to sequences surrounding tRNAOther. This suggested that tRNAOther might be expressed as part of a larger RNA, and RACE analysis subsequently confirmed the existence of several RNA species that significantly extend both the 3′ and 5′-ends of tRNAOther. tRNAOther expression levels were found to be responsive to changes in extracellular iron concentration, consistent with the presence of three putative ferric uptake regulator (Fur) binding sites in the 5′ leader region of one of these larger RNAs. Taken together with previous data, this study now suggests that tRNAOther may function by providing a tRNA-like structural element within a larger regulatory RNA. These findings illustrate that while integration of genomic islands often leaves tRNA genes intact and functional, in other instances inactivation may generate tRNA-like elements that are then recruited to other functions in the cell.
Highlights
TRNAs are essential for accurate translation of the genetic code, during which the anticodon of an aminoacylated tRNA is paired with the corresponding mRNA codon
Previous studies showed that tRNAOther can be aminoacylated with lysine in vitro, albeit poorly [17], prompting us to test for tRNAOther-dependent lysylation of membrane lipids which could be expected to influence antibiotic resistance [5,20,21]
No differences were observed in either total lipid synthesis or the degree of membrane lysylation in wild-type relative to B. cereus DtRNAOther, indicating that tRNAOther does not function in tRNA-dependent lipid modification
Summary
TRNAs are essential for accurate translation of the genetic code, during which the anticodon of an aminoacylated tRNA is paired with the corresponding mRNA codon. Genes encoding tRNAs that function within translation can be predicted with various software programs such as tRNAscan-SE, ARAGORN and TFAM, which classify tRNAs by their anticodon sequence, predicted secondary structure, and additional identity elements [1,2,3]. These bioinformatics approaches have led to the identification of large families of tRNAs, which in many organisms exceed the expected needs for translation alone. Canonical tRNA structures do not mark larger RNAs for aminoacylation but instead provide protein-binding sites that impart a broad range of functions [11,12,13]
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