MEDIUM-DEPENDENT REGULATION OF PROTEINASE GENE-EXPRESSION IN LACTOCOCCUS-LACTIS - CONTROL OF TRANSCRIPTION INITIATION BY SPECIFIC DIPEPTIDES

Transcriptional gene fusions with the Escherichia coli beta-glucuronid ase gene (gusA) were used to study the medium- and growth-dependent ex pression of the divergently transcribed genes involved in proteinase p roduction (prtP and prtM) of Lactococcus lactis SK11. The results show that both the prtP and prtM genes are controlled at the transcription al level by the peptide content of the medium and, to a lesser extent, by the growth rate. A more than 10-fold regulation in beta-glucuronid ase activity was observed for both prtP and prtM promoters in batch an d continuous cultures. The level of expression of the prtP and prtM pr omoters was high in whey permeate medium with relatively low concentra tions of peptides, whereas at increased concentrations the expression of the promoters was repressed. The lowest level of expression was obs erved in peptide- and amino acid-rich laboratory media, such as glucos e-M17 and MRS. The addition of specific dipeptides, such as leucylprol ine and prolylleucine, to the growth medium negatively affected the ex pression of the prtP-gusA fusions. The repression by dipeptides was no t observed in mutants defective in the uptake of di-tripeptides, indic ating that the internal concentration of dipeptides or derivatives is important in the regulation of proteinase production.