The invention relates to vectors and mammalian cells in a system useful for switching on or switching off gene expression in response to uric acid. In a particular embodiment the invention relates to a mammalian cell useful in detecting and/or degrading a harmful excess of uric acid comprising (a) a vector comprising a genetic code for the uricase sensor-regulator HucR from Deinococcus radiodurans R1 fused to a transactivation domain or a transrepressor domain; and (b) a vector comprising the corresponding operator sequence hucO from Deinococcus radiodurans R1 specifically binding the bacterial uric acid sensor-regulator HucR, a promoter and a polynucleotide coding for an endogenous or exogenous protein, e.g. a protein interacting with uric acid.