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J. Bacteriol., Jul 1996, 3689-3694, Vol 178, No. 13
SM Madsen, B Albrechtsen, EB Hansen and H Israelsen
Two genes, hom and thrB, involved in threonine biosynthesis in Lactococcus
lactis MG1614, were cloned and sequenced. These genes, which encode
homoserine dehydrogenase and homoserine kinase, were initially identified
by the homology of their gene products with known homoserine dehydrogenases
and homoserine kinases from other organisms. The identification was
supported by construction of a mutant containing a deletion in hom and thrB
that was unable to grow in a defined medium lacking threonine.
Transcriptional analysis showed that the two genes were located in a
bicistronic operon with the order 5' hom-thrB 3' and that transcription
started 66 bp upstream of the translational start codon of the hom gene. A
putative -10 promoter region (TATAAT) was located 6 bp upstream of the
transcriptional start point, but no putative -35 region was identified. A
DNA fragment covering 155 bp upstream of the hom translational start site
was functional in pAK80, an L. lactis promoter probe vector. In addition,
transcriptional studies showed no threonine-dependent regulation of
hom-thrB transcription.
Copyright © 1996, American Society for Microbiology
Cloning and transcriptional analysis of two threonine biosynthetic genes from Lactococcus lactis MG1614
Department of Research and Development, Biotechnological Institute, Denmark.
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