Contribution of nonconsensus base pairs within ArsR binding sequences toward ArsR-DNA binding and arsenic-mediated transcriptional induction

BACKGROUND: A transcriptional reporter is the key component in bacterial biosensors which are employed to monitor the induction or repression of a reporter gene corresponding to environmental change. Interaction of a transcription factor with its consensus sequence generated by using a position weight matrix (PWM) model is crucial for its sensitivity of the reporter. However, recent studies suggest that PWM model based on independent contribution of individual consensus base pairs to protein interaction is often insufficient to explain complex regulation, such as the effect of nonconsensus sequences on the protein-DNA binding affinity. In the present study, we employed a simpler prokaryotic arsenic repressor (ArsR) regulation system to access the protein-DNA recognition. Contribution of nonconsensus base pairs within ArsR binding sequences toward ArsR-DNA binding and arsenic-mediated transcriptional induction was studied. RESULTS: We constructed a series of arsenic responsive reporters, each comprising two copies of the ArsR binding sequences from different resources. We found that high arsenic-mediated induction specifically requires the binding sequence from Escherichia coli to be placed at the first binding sequence; however, no such preference was observed for the second binding sequence, which could be from Acidithiobacillus ferrooxidans, plasmid R773, Synechococcus, or a core binding sequence of arsR. By creating a series of reporters differed at the nonconsensus base pairs of the second binding sequence, we observed that some constructs bound weakly while others strongly to ArsR. Most interestingly, although a number of these reporters showed similar binding affinity to ArsR, their arsenic-dependent induction differed significantly. CONCLUSIONS: The results indicated that nonconsensus base pairs could have profound influence on protein binding and may also modulate post-binding function. These findings provide new insights into the complex regulation of gene expression and facilitate the development of transcriptional reporter-based biosensors.