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Journal of Bacteriology, February 1999, p. 858-868, Vol. 181, No. 3
Institute of Biotechnology, ETH
Hönggerberg, CH-8093 Zürich, Switzerland
Received 9 September 1998/Accepted 21 November 1998
The phaC1 gene codes for the medium-chain-length
polyhydroxyalkanoate (mcl PHA) synthase of Pseudomonas
oleovorans GPo1, which produces mcl PHA when grown in an excess
of carbon source and under nitrogen limitation. In this work, we have
demonstrated, by constructing a recombinant P. oleovorans
strain carrying a phaC1::lacZ
reporter system, that the phaC1 gene is expressed efficiently in the presence of octanoic acid while its expression is
repressed when glucose or citrate is used as the carbon source. Moreover, a P. oleovorans GPo1 mutant (strain GPG-Tc6)
expressing higher levels of the reporter gene than the wild-type strain
in the presence of glucose or citrate has been generated by
mini-Tn5 insertional mutagenesis. Characterization of this
mutant allowed us to conclude that phaF, a gene located
downstream of the pha gene cluster, was knocked out in this
strain. P. oleovorans GPG-Tc6 regained the ability to
control phaC1 gene expression when complemented with the
phaF wild-type gene. Sequencing data revealed the presence of three complete open reading frames (ORFs) in this region: ORF1 and
phaI and phaF genes. The amino acid sequences
of the phaI gene product and the N-terminal half of the
PhaF protein showed a significant degree of similarity. Furthermore,
the primary structure of the PhaF C terminus identifies this protein as
a member of the histone H1-like group of proteins. Northern blot
analysis showed two transcription units containing phaF,
i.e., phaF and phaIF transcripts. Expression of
the phaIF operon is more efficient in the presence of
octanoic acid and is enhanced by the lack of the PhaF protein. In
addition, it has also been demonstrated that both PhaF and PhaI
proteins are bound to PHA granules produced by P. oleovorans. A model for the role of PhaF in regulating PHA synthesis is presented.
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
PhaF, a Polyhydroxyalkanoate-Granule-Associated
Protein of Pseudomonas oleovorans GPo1 Involved in the
Regulatory Expression System for pha Genes

*
Corresponding author. Mailing address: Institute of
Biotechnology, ETH Hönggerberg, CH-8093 Zürich,
Switzerland. Phone: 41-1-6333402. Fax: 41-1-6331051. E-mail:
bw{at}biotech.biol.ethz.ch.
Present address: Centro de Investigaciones Biologicas, CSIC
C/Velazquez, 144, 28006 Madrid, Spain.
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