A novel selenite- and tellurite-inducible gene in Escherichia coli

Selenium is both an essential and a toxic trace element, and the range of c oncentrations between the two is extremely narrow. Although tellurium is no t essential and is only rarely found in the environment, it is considered t o be extremely toxic. Several hypotheses have been proposed to account for the toxic effects of selenite and tellurite. However, these potential mecha nisms have yet to be fully substantiated. Through screening of an Escherich ia coli luxAB transcriptional gene fusion library, we identified a clone wh ose luminescence increased in the presence of increasing concentrations of sodium selenite or sodium tellurite, Cloning and sequencing of the luxAB ju nction revealed that the fusion had occurred in a previously uncharacterize d open reading frame, termed o393 or yhfC, which we have now designated gut S, for gene up-regulated by tellurite and selenite, Transcription from gutS in the presence of selenite or tellurite was confirmed by RNA dot blot ana lysis, In vivo expression of the GutS polypeptide, using the pET expression system, revealed a polypeptide of approximately 43 kDa, in good agreement with its predicted molecular mass. Although the function of GutS remains to be elucidated, homology searches as well as protein motif and secondary-st ructure analyses have provided clues which may implicate GutS in transport in response to selenite and tellurite.