D. Nilsson et M. Kilstrup, CLONING AND EXPRESSION OF THE LACTOCOCCUS-LACTIS PURDEK GENES, REQUIRED FOR GROWTH IN MILK, Applied and environmental microbiology (Print), 64(11), 1998, pp. 4321-4327
An operon containing the genes purD and purE and part of the purK gene
was cloned from the facultative anaerobic gram positive bacterium Lac
tococcus lactis by complementation of the purD mutation in Escherichia
coli SO609. The genes encode enzymes in the de novo pathway of purine
nucleotides. The expression of the genes was regulated approximately
35-fold at the transcription level by the availability of purines in t
he growth medium. Deletion analysis of the nucleotide region upstream
of purD indicated that a region of 145 bp is enough to give regulated
expression of the reporter lacLM genes, which encode beta-galactosidas
e. Deletion of a region 79 bp upstream of the transcription start poin
t reduced the promoter activity 33-fold when incubated in a purine-fre
e medium and to values below the detection limit when incubated in a p
urine-containing medium. No secondary transcription start points were
mapped in or close to this region, indicating that a putative activato
r site and not a promoter was deleted or partly destroyed.