Affiliation:
1. Department of Microbiology and Immunology, Emory University School of Medicine, Atlanta, Georgia 30322
Abstract
ABSTRACT
The impressive disease spectrum of
Streptococcus pyogenes
(the group A streptococcus [GAS]) is believed to be determined by its ability to modify gene expression in response to environmental stimuli. Virulence gene expression is controlled tightly by several different transcriptional regulators in this organism. In addition, expression of most, if not all, GAS genes is determined by a global mechanism dependent on growth phase. To begin an analysis of growth-phase regulation, we compared the transcriptome 2 h into stationary phase to that in late exponential phase of a serotype M3 GAS strain. We identified the
arc
transcript as more abundant in stationary phase in addition to the
sag
and
sda
transcripts that had been previously identified. We found that in stationary phase, the stability of
sagA
,
sda
, and
arcT
transcripts increased dramatically. We found that polynucleotide phosphorylase (PNPase [encoded by
pnpA
]) is rate limiting for decay of
sagA
and
sda
transcripts in late exponential phase, since the stability of these mRNAs was greater in a
pnpA
mutant, while stability of control mRNAs was unaffected by this mutation. Complementation restored the wild-type decay rate. Furthermore, in a
pnpA
mutant, the
sagA
mRNA appeared to be full length, as determined by Northern hybridization. It seems likely that mRNAs abundant in stationary phase are insensitive to the normal decay enzyme(s) and instead require PNPase for this process. It is possible that PNPase activity is limited in stationary phase, allowing persistence of these important virulence factor transcripts at this phase of growth.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
60 articles.
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