Unusual organization for lactose and galactose gene clusters in Lactobacillus helveticus.
The nucleotide sequences of the Lactobacillus helveticus lactose utilization genes were determined, and these genes were located and oriented relative to one another. The lacLM genes (encoding the beta-galactosidase protein) were in a divergent orientation compared to lacR (regulatory gene) and lacS (lactose transporter). Downstream from lacM was an open reading frame (galE) encoding a UDP-galactose 4 epimerase, and the open reading frame had the same orientation as lacM. The lacR gene was separated from the downstream lacS gene by 2.0 kb of DNA containing several open reading frames that were derived from fragmentation of another permease gene (lacS'). Northern blot analysis revealed that lacL, lacM, and galE made up an operon that was transcribed in the presence of lactose from an upstream lacL promoter. The inducible genes lacL and lacM were regulated at the transcriptional level by the LacR repressor. In the presence of glucose and galactose galE was transcribed from its promoter, suggesting that the corresponding enzyme can be expressed constitutively. Lactose transport was inducible by addition of lactose to the growth medium.
Fortina
Maria Grazia
MG
Industrial Microbiology Section, Department of Food Science and Microbiology, University of Milan, 20133 Milan, Italy. grazia.fortina@unimi.it
Ricci
Giovanni
G
Mora
Diego
D
Guglielmetti
Simone
S
Manachini
Pier Luigi
PL
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D005690:Galactose / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D007778:Lactobacillus / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D007785:Lactose / Q000378:metabolism*; D008969:Molecular Sequence Data; D005810:Multigene Family; D017422:Sequence Analysis, DNA; D014158:Transcription, Genetic
D001426:Bacterial Proteins; D007785:Lactose; D005690:Galactose