Both RRs are DNA-binding proteins that bind to promoter-proximal elements in the pln regulon.

We demonstrated that the plnABCD operon codes for an autoregulatory unit capable of activating its own promoter.

How phosphorylation regulates the activity of the pln response regulators was also accessed by direct mutagenesis at their phosphorylation sites.

This raises the question whether a functional peptide is being produced, even though RT-PCR studies showed that the plnE gene is obviously expressed.

Furthermore, heterologous expression of the plnABCD operon in a Lactobacillus sake strain showed that the conditioned growth medium contained the active induction factor.