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J. Bacteriol., 05 1995, 2408-2415, Vol 177, No. 9
O Egeter and R Bruckner
A genetic locus from Staphylococcus xylosus involved in maltose-
maltotriose utilization has been characterized. The chromosomal region was
identified by screening a genomic library of S. xylosus in Escherichia coli
for sucrose hydrolase activity. Nucleotide sequence analysis yielded two
open reading frames (malR and malA) encoding proteins of 37.7 and 62.5 kDa,
respectively. MalR was found to be homologous to the LacI-GalR family of
transcriptional regulators, and MalA showed high similarity to yeast
alpha-1,4-glucosidases and bacterial alpha-1,6-glucosidases. Inactivation
of malA in the genome of S. xylosus led to a maltose-maltotriose-negative
phenotype. In cell extracts of the mutant, virtually no glucose release
from maltose and short maltodextrins was detectable. Inactivation of malA
in a sucrose-6- phosphate hydrolase-deficient S. xylosus strain resulted in
the complete loss of the residual sucrose hydrolase activity. The MalA
enzyme has a clear preference for maltose but is also able to release
glucose from short maltosaccharides. It cannot cleave isomaltose.
Therefore, malA encodes an alpha-1,4-glucosidase or maltase, which also
liberates glucose from sucrose. Subcloning experiments indicated that malA
does not possess its own promoter and is cotranscribed with malR. Its
expression could not be stimulated when maltose was added to the growth
medium. Chromosomal inactivation of malR led to reduced maltose
utilization, although alpha-glucosidase activity in the malR mutant was
slightly higher than in the wild type. In the mutant strain, maltose uptake
was reduced and inducibility of the transport activity was partially lost.
It seems that MalR participates in the regulation of the gene(s) for
maltose transport and is needed for their full expression.(ABSTRACT
TRUNCATED AT 250 WORDS)
Copyright © 1995, American Society for Microbiology
Characterization of a genetic locus essential for maltose-maltotriose utilization in Staphylococcus xylosus
Universitat Tubingen, Germany.
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