van Rooijen R J, Gasson M J, de Vos W M
Department of Biophysical Chemistry, Netherlands Institute for Dairy Research (NIZO), Ede.
J Bacteriol. 1992 Apr;174(7):2273-80. doi: 10.1128/jb.174.7.2273-2280.1992.
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).
我们确定了乳酸乳球菌8 kb乳糖操纵子（lacABCDFEGX）启动子的位置、活性和调控方式，该操纵子编码乳糖磷酸转移酶系统和塔格糖6-磷酸途径的酶。lac启动子序列与革兰氏阳性菌中描述的共有启动子密切对应，并且与反向转录的lacR基因（编码LacR阻遏物）的启动子呈背对背排列。确定了在诱导（乳糖）和非诱导（葡萄糖）条件下使用的转录起始位点。可以在单个限制片段上分离的最小启动子区域包括从-75到+42的序列。通过使用无启动子氯霉素乙酰转移酶报告基因的转录融合，在大肠杆菌和乳酸乳球菌菌株中研究了侧翼序列和lacR基因的存在对启动子活性和调控的影响。结果表明，lac操纵子的转录调控是由LacR阻遏物、lac启动子以及lacR和lacA基因之间非编码区域中的序列之间的相互作用介导的。最小启动子区域侧翼的序列在乳酸乳球菌中（5至38倍）比在大肠杆菌中（1.3至5倍）似乎更能增强lac启动子活性。
