Affiliation:
1. Department of Biology
2. Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
Abstract
ABSTRACT
Polyhydroxyalkanoates (PHAs) are polyoxoesters that are produced by many bacteria and that accumulate as intracellular granules. Phasins (PhaP) are proteins that accumulate during PHA synthesis, bind PHA granules, and promote further PHA synthesis. Interestingly, PhaP accumulation seems to be strictly dependent on PHA synthesis, which is catalyzed by the PhaC PHA synthase. Here we have tested the effect of the
Ralstonia eutropha
PhaR protein on the regulation of PhaP accumulation.
R. eutropha
strains with
phaR
,
phaC
, and/or
phaP
deletions were constructed, and PhaP accumulation was measured by immunoblotting. The wild-type strain accumulated PhaP in a manner dependent on PHA production, and the
phaC
deletion strain accumulated no PhaP, as expected. In contrast, both the
phaR
and the
phaR phaC
deletion strains accumulated PhaP to higher levels than did the wild type. This result implies that PhaR is a negative regulator of PhaP accumulation and that PhaR specifically prevents PhaP from accumulating in cells that are not producing PHA. Transfer of the
R. eutropha phaR
,
phaP
, and PHA biosynthesis (
phaCAB
) genes into a heterologous system,
Escherichia coli
, was sufficient to reconstitute the PhaR/PhaP regulatory system, implying that PhaR both regulates PhaP accumulation and responds to PHA directly. Deletion of
phaR
caused a decrease in PHA yields, and a
phaR phaP
deletion strain exhibited a more severe PHA defect than a
phaP
deletion strain, implying that PhaR promotes PHA production and does this at least partially through a PhaP-independent pathway. Models for regulatory roles of PhaR in regulating PhaP and promoting PHA production are presented.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
142 articles.
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