Abstract: The invention concerns a novel construct for expressing a gene coding for a recombinant protein of interest placed under the control of the Ptrp tryptophan operon promoter in a procaryotic host cell. The invention is characterised in that the construct comprises a nucleic sequence capable of inactivating the gene coding for a TnaA tryptophanase when said nucleic sequence is introduced in said host cell. The invention also concerns vectors containing said construct and host cells transformed by said vectors. The invention further concerns methods for producing said recombinant proteins using said novel constructs.