Transcriptional pattern of genes coding for the proteolytic system of Lactococcus lactis and evidence for coordinated regulation of key enzymes by peptide supply

The transcription of 16 genes encoding 12 peptidases (pepC, pepN, pepX, pep P, pepA, pepF2, pepDA1, pepDA2, pepQ, pepT, pepM and pepO1), P-I and P-III proteinases (prtP1 and prtP3), and three transport systems (dtpT, dtpP, and opp-pepO1) of Lactococcus lactis MG1363 was analyzed in response to differ ent environmental factors. Promoter fusions with luciferase reporter genes and/or mRNA analysis were used to study the effects of sugar sources, growt h at 37 degreesC, and peptide supply on the transcription of these genes. O nly transcription of the pepP gene is modulated by the source of sugar. The presence of potential catabolite-responsive element (CRE) boxes in its pro moter region suggests that expression of this gene is directly controlled b y catabolic repression. Elevated temperature had no significant effect on t he level of transcription of these genes. prtP1, prtP3, pepC, pepN: pepX, a nd the opp-pepO1 operon are the most highly expressed genes in chemically d efined medium, and their expression is repressed 5- to 150-fold by addition of peptide sources such as Casitone in the medium. Moreover, the transcrip tion of prtP1, prtP3, pepC, pepN, and the opp-pepO1 operon is repressed two - to eight-fold by the dipeptides leucytproline and prolylleucine. The tran scription of pepDA2 might also be repressed by the peptide sources, but thi s effect is not observed on the regulation of dtpT, pepP, pepA, pepF2, pepD A1 pepQ, pepT, pepM, and the dtpP operon. The significance of these results with respect to the functions of different components of the proteolytic s ystem in L. lactis are discussed.