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J. Bacteriol., 02 1997, 714-720, Vol 179, No. 3
M Hagemann, S Richter and S Mikkat
The ggtA gene was sequenced during the analysis of a mutant of
Synechocystis sp. strain PCC 6803 with impaired salt tolerance. It showed
striking sequence similarities to ATP-binding proteins of
binding-protein-dependent transport systems (ABC transporters). Mutants of
ggtA and three neighboring reading frames were constructed by inserting an
aphII gene cassette and were physiologically and genetically characterized.
The ggtA insertion mutant lost its glucosylglycerol (GG) uptake ability,
but its salt tolerance did not change. Therefore, it was concluded that
active transport of the osmoprotective compound GG in Synechocystis is
mediated by an ABC transporter. The genes for the GG-specific ABC
transporter are not organized in an operon as usually found for comparable
transporters, since the other insertion mutants showed normal GG transport
activity. After cultivation of the ggtA mutant at high salt concentrations,
significant amounts of GG were found in the cultivation medium, indicating
that GG transport is mainly necessary for recovery of GG leaked through the
cytoplasmic membrane. The Northern blot technique revealed increased
transcription of the ggtA gene in cells adapted to higher salt
concentrations, whereas in cells from basal medium, its transcription was
weak.
Copyright © 1997, American Society for Microbiology
The ggtA gene encodes a subunit of the transport system for the osmoprotective compound glucosylglycerol in Synechocystis sp. strain PCC 6803
Fachbereich Biologie, Universitat Rostock, Germany. mh@boserv.bio4.uni- rostock.de
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