Sequence, organization, transcription and regulation of lactose and galactose operons in Lactobacillus rhamnosus TCELL-1.
OBJECTIVE
Understanding the metabolism of lactose and galactose and their regulation in Lactobacillus rhamnosus.


RESULTS
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.


CONCLUSIONS
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.


CONCLUSIONS
This work provides important information about sugar metabolism in Lact. rhamnosus.
Tsai
Y-K
YK
Institute of Molecular Medicine and Department of Life Science, National Tsing Hua University, Hsinchu, Taiwan.
Lin
T-H
TH
D000595:Amino Acid Sequence; D001483:Base Sequence; D005690:Galactose / Q000235:genetics* / Q000378:metabolism; D005786:Gene Expression Regulation / Q000235:genetics; D007763:Lac Operon / Q000235:genetics; D052201:Lacticaseibacillus rhamnosus / Q000235:genetics* / Q000254:growth & development; D007785:Lactose / Q000235:genetics* / Q000378:metabolism; D005810:Multigene Family / Q000235:genetics*; D016366:Open Reading Frames / Q000235:genetics; D009876:Operon / Q000235:genetics*; D011401:Promoter Regions, Genetic / Q000235:genetics; D012329:RNA, Bacterial / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics; D017421:Sequence Analysis / Q000379:methods; D014158:Transcription, Genetic / Q000235:genetics; D001616:beta-Galactosidase / Q000032:analysis
D012329:RNA, Bacterial; D012333:RNA, Messenger; D001616:beta-Galactosidase; D007785:Lactose; D005690:Galactose