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J. Bacteriol., 04 1997, 2658-2667, Vol 179, No. 8
U Mechold and H Malke
The 739-codon rel(Seq) gene of Streptococcus equisimilis H46A is
bifunctional, encoding a strong guanosine 3',5'-bis(diphosphate) 3'-
pyrophosphohydrolase (ppGppase) and a weaker ribosome-independent ATP:GTP
3'-pyrophosphoryltransferase [(p)ppGpp synthetase]. To analyze the function
of this gene, (p)ppGpp accumulation patterns as well as protein and RNA
synthesis were compared during amino acid deprivation and glucose
exhaustion between the wild type and an insertion mutant carrying a
rel(Seq) gene disrupted at codon 216. We found that under normal
conditions, both strains contained basal levels of (p)ppGpp. Amino acid
deprivation imposed by pseudomonic acid or isoleucine hydroxamate triggered
a rel(Seq)-dependent stringent response characterized by rapid (p)ppGpp
accumulation at the expense of GTP and abrupt cessation of net RNA
accumulation in the wild type but not in the mutant. Tetracycline added to
block (p)ppGpp synthesis caused the accumulated (p)ppGpp to degrade
rapidly, with a concomitant increase of the GTP pool (decay constant of
ppGpp, approximately 0.7 min(-1)). Simultaneous addition of pseudomonic
acid and tetracycline to mimic a relaxed response caused wild-type RNA
synthesis to proceed at rates approximating those seen under either
condition in the mutant. Glucose exhaustion provoked the (p)ppGpp
accumulation response in both the wild type and the rel(Seq) insertion
mutant, consistent with the block of net RNA accumulation in both strains.
Although the source of (p)ppGpp synthesis during glucose exhaustion remains
to be determined, these findings reinforce the idea entertained previously
that rel(Seq) fulfils functions that reside separately in the paralogous
reL4 and spoT genes of Escherichia coli. Analysis of (p)ppGpp accumulation
patterns was complicated by finding an unknown phosphorylated compound that
comigrated with ppGpp under two standard thin-layer chromatography
conditions. Unlike ppGpp, this compound did not adsorb to charcoal and did
not accumulate appreciably during isoleucine deprivation. Like ppGpp, the
unknown compound did accumulate during energy source starvation.
Copyright © 1997, American Society for Microbiology
Characterization of the stringent and relaxed responses of Streptococcus equisimilis
Institute for Molecular Biology, Jena University, Germany.
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