Abstract
BackgroundTransposable elements (TEs) are a diverse group of self-mobilizing DNA elements. Transposition has been exploited as a powerful tool for molecular biology and genomics. However, transposition is sometimes limited because of auto-regulatory mechanisms that presumably allow them to cohabit within their hosts without causing excessive genomic damage. The papillation assay provides a powerful visual screen for hyperactive transposases. Transposition is revealed by the activation of a promoter-less lacZ gene when the transposon integrates into a non-essential gene on the host chromosome. Transposition events are detected as small blue speckles, or papillae, on the white background of the main Escherichia coli colony.ResultsWe analysed the parameters of the papillation assay including the strength of the transposase transcriptional and translational signals. To overcome certain limitations of inducible promoters, we constructed a set of vectors based on constitutive promoters of different strengths to widen the range of transposase expression. We characterized and validated our expression vectors with Hsmar1, a member of the mariner transposon family. The highest rate of transposition was observed with the weakest promoters. We then took advantage of our approach to investigate how the level of transposition responds to selected point mutations and the effect of joining the transposase monomers into a single-chain dimer.ConclusionsWe generated a set of vectors to provide a wide range of transposase expression which will be useful for screening libraries of transposase mutants. The use of weak promoters should allow screening for truly hyperactive transposases rather than those that are simply resistant to auto-regulatory mechanisms, such as overproduction inhibition (OPI). We also found that mutations in the Hsmar1 dimer interface provide resistance to OPI in bacteria, which could be valuable for improving bacterial transposon mutagenesis techniques.
Highlights
Transposable elements (TEs) are a diverse group of self-mobilizing DNA elements
We found that one Hsmar1 mutant in the dimer interface, R141L, is resistant to overproduction inhibition (OPI) in E. coli
Characterization of the papillation assay using a strong inducible promoter The papillation assay provides a visual assessment of the transposition rate, which is dependent on the concentration and activity of the transposase [12, 20]
Summary
Transposable elements (TEs) are a diverse group of self-mobilizing DNA elements. Transposition has been exploited as a powerful tool for molecular biology and genomics. Transposable elements (TEs) are DNA sequences with the ability to move from one place to another in the genome. They are found in virtually all organisms and are numerous in higher eukaryotes where they can represent a significant percentage of the genome [1,2,3]. OPI curbs Hsmar transposition rate to avoid damaging the host genome by excessive transposition [12].
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