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Journal of Bacteriology, January 2001, p. 94-100, Vol. 183, No. 1
Research Institute of Innovative Technology
for the Earth Branch in Kanagawa University1
and Laboratory of Molecular Microbiology, Department of
Biological Sciences, Faculty of Science, Kanagawa
University,2 2946 Tsuchiya, Hiratsuka, Kanagawa
259-1293, Japan
Received 14 August 2000/Accepted 10 October 2000
An intracellular poly[D(
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.1.94-100.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Cloning of an Intracellular
Poly[D(
)-3-Hydroxybutyrate] Depolymerase
Gene from Ralstonia eutropha H16 and Characterization of the
Gene Product
)-3-hydroxybutyrate] (PHB)
depolymerase gene (phaZ) has been cloned from
Ralstonia eutropha H16 by the shotgun method, sequenced,
and characterized. Nucleotide sequence analysis of a 2.3-kbp DNA
fragment revealed an open reading frame of 1,260 bp, encoding a protein
of 419 amino acids with a predicted molecular mass of 47,316 Da. The
crude extract of Escherichia coli containing the PHB
depolymerase gene digested artificial amorphous PHB granules and
released mainly oligomeric D(
)-3-hydroxybutyrate, with
some monomer. The gene product did not hydrolyze crystalline PHB or
freeze-dried artificial amorphous PHB granules. The deduced amino acid
sequence lacked sequence corresponding to a classical lipase box,
Gly-X-Ser-X-Gly. The gene product was expressed in R. eutropha cells concomitant with the synthesis of PHB and
localized in PHB granules. Although a mutant of R. eutropha
whose phaZ gene was disrupted showed a higher PHB content
compared to the wild type in a nutrient-rich medium, it accumulated PHB
as much as the wild type did in a nitrogen-free, carbon-rich medium.
These results indicate that the cloned phaZ gene encodes an
intracellular PHB depolymerase in R. eutropha.
*
Corresponding author. Mailing address: Laboratory of
Molecular Microbiology, Department of Biological Sciences, Faculty of Science, Kanagawa University, 2946 Tsuchiya, Hiratsuka, Kanagawa 259-1293, Japan. Phone: 81-463-59-4111. Fax: 81-463-58-9684. E-mail: 43saito{at}info.kanagawa-u.ac.jp.
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