Two-component signal transduction is a common mechanism by which bacteria sense and
respond to environmental stimuli [17]. The two components comprise a sensor histidine kinase
protein, which typically contains periplasmic receptor and cytoplasmic kinase/phosphatase
domains, and a response regulator protein. The sensor kinase senses the stimulus, which
results in the transfer of a phosphoryl group from its cytoplasmic domain to an aspartate residue
on the response regulator receiver domain. Phosphorylation of the response regulator receiver
domain results in activation of its output domain. An active response regulator typically
achieves its goal by directly altering bacterial transcription of genes necessary for response to
the original stimulus [18]. Two-component regulation is ubiquitous within the prokaryotic domain,
with the numbers of two component proteins varying among bacteria from only a few to
over 250 proteins (E. coli has and 29 sensor kinases and 32 response regulators) [18]. Our
study shows that the introduction of a foreign response regulator gene into E. coli can directly
impact gene expression, leading to an antibiotic resistance phenotype.