Tsai Y-K, Lin T-H
Institute of Molecular Medicine and Department of Life Science, National Tsing Hua University, Hsinchu, Taiwan.
J Appl Microbiol. 2006 Mar;100(3):446-59. doi: 10.1111/j.1365-2672.2005.02790.x.
Understanding the metabolism of lactose and galactose and their regulation in Lactobacillus rhamnosus.
A gene cluster containing nine open reading frames (ORFs) involved in the metabolism of lactose and galactose in Lact. rhamnosus TCELL-1 was sequenced and characterized. The order of the ORFs was lacTEGF and galKETRM. Northern blotting experiments revealed that the gene cluster could be transcribed as one lacTEGF-galKETRM mRNA though three major transcripts (lacTEGF, galKETRM and galETRM) were detected for the gene cluster. The transcription of the lac or gal operon was independently induced in the presence of lactose or galactose. Northern blotting and primer extension experiments found the presence of four putative promoters upstream from the ORFs lacT (lacTp), galK (galKp1 and galKp2) and galE (galEp). The measurements of enzymatic activities of GalK, GalE and GalT suggested that the expression of the gal operon was subjected to a galactose activation and glucose repression mechanism.
In Lact. rhamnosus TCELL-1, the galactose moiety of lactose could be metabolized by two alternative pathways (the Leloir and the tagatose 6-phosphate pathways) whereas galactose metabolism could be mediated by the Leloir pathway.
This work provides important information about sugar metabolism in Lact. rhamnosus.
了解鼠李糖乳杆菌中乳糖和半乳糖的代谢及其调控机制。
对鼠李糖乳杆菌TCELL-1中一个包含9个开放阅读框（ORF）的基因簇进行了测序和表征，该基因簇参与乳糖和半乳糖的代谢。ORF的顺序为lacTEGF和galKETRM。Northern印迹实验表明，尽管检测到该基因簇有三种主要转录本（lacTEGF、galKETRM和galETRM），但该基因簇可转录为一种lacTEGF-galKETRM mRNA。在乳糖或半乳糖存在的情况下，lac或gal操纵子的转录是独立诱导的。Northern印迹和引物延伸实验发现，在ORF lacT（lacTp）、galK（galKp1和galKp2）和galE（galEp）上游存在四个假定的启动子。GalK、GalE和GalT的酶活性测定表明，gal操纵子的表达受半乳糖激活和葡萄糖抑制机制的调控。
在鼠李糖乳杆菌TCELL-1中，乳糖的半乳糖部分可通过两条替代途径（Leloir途径和磷酸塔格糖途径）进行代谢，而半乳糖代谢可由Leloir途径介导。
这项工作提供了有关鼠李糖乳杆菌糖代谢的重要信息。
