The present invention relates to a cell comprising a first nucleic acid sequence encoding a first polypeptide fused to the N-terminus of a first variant of a histidine kinase comprising a DHp domain and a CA domain, wherein said first variant does not comprise a transmembrane domain, a second nucleic acid sequence encoding a second polypeptide fused to the N-terminus of a second variant of said histidine kinase comprising a DHp domain and a CA domain, wherein said second variant does not comprise a transmembrane domain, and a third nucleic acid sequence encoding a response regulatory protein specifically phosphorylatable by said DHp domain of said first or said second variant. The present invention further relates to uses of the cell of the invention.