An expression cassette comprising: a) a bacterial promoter, pZn, containing a binding site for the Lactococcus lactis ZitR protein, which site comprises the following sequence: AAAAATAANGTNNNNNNNTTGACATTATTTTT,(SEQ ID NO: 1) in which TTGACA is the −35 box of said promoter, and N represents A, C, G or T; b) a sequence encoding a polypeptide with at least 80% identity with the Lactococcus lactis ZitR protein, placed under the transcriptional control of said promoter; and wherein the polypeptide is obtained from Lactococcus; and c) at least one restriction site allowing the insertion of a nucleotide sequence of interest under the transcriptional control of said promoter, and wherein the expression cassette does not comprise any part of the sequence encoding the L. lactis ZitS protein.