Effects on IS1transposition frequency of a mutation in theygjDgene involved in an essential tRNA modification inEscherichia coli

Abstract

The YgjD protein is essential for the synthesis of the universal tRNA modification, N(6) -threonylcarbamoyladenosine (t(6) A), which is necessary for the decoding of ANN codons. We isolated a suppressor (ygjDsup ) of the ygjD(ts) mutant by its permissive growth at high temperature in Escherichia coli. Resequencing of the ygjDsup mutant genome showed the presence of a complicated chromosome rearrangement, an inverse insertion of a large duplicated region (c. 450 kb) into a small deleted region. The temperature-resistant growth associated with ygjDsup was due to the presence of multicopy suppressor genes, yjeE and groL, of the ygjD(ts) mutation in the duplicated region. This DNA rearrangement was not simply mediated by IS1 transposition, but the duplicated region was flanked by IS1. We showed that the frequency of IS1 transposition was increased in ygjD(ts) mutants. The transposase of IS1 is coded for by the insB gene, and its translation occurs through a frameshift of a ribosome translating upstream of the insA gene. We showed that this frameshifting frequency was increased by the ygjD(ts) mutation. These results indicated that the mutation of the gene for tRNA modification, t(6) A, affected IS1 transposition.

Essentiality of threonylcarbamoyladenosine (t6A), a universal tRNA modification, in bacteria

“…This suggested that these genes belonged to a complex regulatory network (Msadek, ), but the rstA suppression phenotype has never been really explained. Overexpression of other genes such as rho , encoding a transcription terminator, or dnaG , encoding DNA primase, have also been reported to suppress the essentiality phenotype caused by depletion of the t 6 A synthesis enzymes (Hashimoto et al ., 2011; 2013; Bergmiller et al ., ), but it is unknown if t 6 A is absent from tRNA isolated from these suppressor strains. Lack of t 6 A‐modificed tRNA in these strains would compromise the development of antibacterials targeting the enzymes of t 6 A machinery, as resistant clones could be selected at a high frequency.…”

Influence of Redox Imbalances on the Transposition of Insertion Sequences in Deinococcus geothermalis

“…Mitomycin C and gamma-irradiation resulted in IS transposition in D. radiodurans [48][49][50][51]. When the translation error rate was enhanced by mutation of ygjD and rpsL encoding the universal tRNA and rRNA modifying proteins, respectively, or under high glucose growth conditions, active transposition of an IS1 family member was found in Escherichia coli [47,52]. Additionally, nutritional stress and host factors have been implicated in the transposition of ISs and TEs [53,54].…”