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J. Bacteriol., 03 1997, 1563-1572, Vol 179, No. 5
PJ Crowley, JA Gutierrez, JD Hillman and AS Bleiweis
Previously we reported that transposon Tn917 mutagenesis of Streptococcus
mutans JH1005 yielded an isolate detective in its normal ability to produce
a mutacin (P. J. Crowley, J. D. Hillman, and A. S. Bleiweis, abstr. D55, p.
258 in Abstracts of the 95th General Meeting of the American Society for
Microbiology 1995, 1995). In this report we describe the recovery of the
mutated gene by shotgun cloning. Sequence analysis of insert DNA adjacent
to Tn917 revealed homology to the gene encoding formyl-tetrahydrofolate
synthetase (Fhs) from both prokaryotic and eukaryotic sources. In many
bacteria, Fhs catalyzes the formation of 10-formyl-tetrahydrofolate, which
is used directly in purine biosynthesis and formylation of Met-tRNA and
indirectly in the biosynthesis of methionine, serine, glycine, and thymine.
Analysis of the fhs mutant grown anaerobically in a minimal medium
demonstrated that the mutant had an absolute dependency only for adenine,
although addition of methionine was necessary for normal growth.
Coincidently it was discovered that the mutant was sensitive to acidic pH;
it grew more slowly than the parent strain on complex medium at pH 5.
Complementation of the mutant with an integration vector harboring a copy
of fhs restored its ability to grow in minimal medium and at acidic pH as
well as to produce mutacin. This represents the first characterization of
Fhs in Streptococcus.
Copyright © 1997, American Society for Microbiology
Genetic and physiologic analysis of a formyl-tetrahydrofolate synthetase mutant of Streptococcus mutans
Department of Oral Biology, University of Florida, Gainesville 32610, USA. crowley@dental.ufl.edu
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