Characterization of the Lactococcus lactis lactose operon promoter: contribution of flanking sequences and LacR repressor to promoter activity.
We determined the location, activity, and regulation of the promoter of the Lactococcus lactis 8-kb lactose operon (lacABCDFEGX), which encodes the enzymes of the lactose phosphotransferase system and the tagatose 6-phosphate pathway. The lac promoter sequence corresponds closely to the consensus promoter described for gram-positive bacteria and is located in a back-to-back configuration with the promoter of the divergently transcribed lacR gene, which encodes the LacR repressor. The transcription start sites used under induced (lactose) and noninduced (glucose) conditions were determined. The minimal promoter region that could be isolated on a single restriction fragment included sequences ranging from -75 to +42. The effect of the presence of flanking sequences and the lacR gene on promoter activity and regulation was studied in Escherichia coli and L. lactis strains by using transcriptional fusions with promoterless chloramphenicol acetyltransferase reporter genes. The results showed that transcriptional regulation of the lac operon is mediated by the interaction between the LacR repressor, the lac promoter, and sequences in the noncoding region between the lacR and lacA genes. Sequences flanking the minimal promoter region appeared to enhance lac promoter activity much more in L. lactis (5- to 38-fold) than in E. coli (1.3- to 5-fold).
van Rooijen
R J
RJ
Department of Biophysical Chemistry, Netherlands Institute for Dairy Research (NIZO), Ede.
Gasson
M J
MJ
de Vos
W M
WM
D001483:Base Sequence; D002874:Chromosome Mapping; D004269:DNA, Bacterial / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D006860:Hydrogen Bonding; D007763:Lac Operon; D013294:Lactococcus lactis / Q000235:genetics*; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D011401:Promoter Regions, Genetic; D012329:RNA, Bacterial / Q000648:ultrastructure; D012333:RNA, Messenger / Q000648:ultrastructure; D012097:Repressor Proteins / Q000235:genetics*; D015183:Restriction Mapping; D012689:Sequence Homology, Nucleic Acid; D014158:Transcription, Genetic
D004269:DNA, Bacterial; D012329:RNA, Bacterial; D012333:RNA, Messenger; D012097:Repressor Proteins