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J Bacteriol, March 1998, p. 1460-1465, Vol. 180, No. 6
Institute of Biophysics,
Received 24 September 1997/Accepted 10 January 1998
The characterization of a hyd gene cluster encoding the
stable, bidirectional [NiFe]hydrogenase 1 enzyme in Thiocapsa
roseopersicina BBS, a purple sulfur photosynthetic bacterium
belonging to the family Chromatiaceae, is presented. The
heterodimeric hydrogenase 1 had been purified to homogeneity and
thoroughly characterized (K. L. Kovacs et al., J. Biol.
Chem. 266:947-951, 1991; C. Bagyinka et al., J. Am. Chem. Soc.
115:3567-3585, 1993). As an unusual feature, a 1,979-bp
intergenic sequence (IS) separates the structural genes
hydS and hydL, which encode the small and the
large subunits, respectively. This IS harbors two sequential open
reading frames (ORFs) which may code for electron transfer proteins
ISP1 and ISP2. ISP1 and ISP2 are homologous to ORF5 and ORF6 in the
hmc operon, coding for a transmembrane electron transfer
complex in Desulfovibrio vulgaris. Other accessory proteins
are not found immediately downstream or upstream of hydSL.
A hup gene cluster coding for a typical hydrogen
uptake [NiFe]hydrogenase in T. roseopersicina was
reported earlier (A. Colbeau et al. Gene 140:25-31, 1994). The deduced
amino acid sequences of the two small (hupS and
hydS) and large subunit (hupL and
hydL) sequences share 46 and 58% identity, respectively.
The hup and hyd genes differ in the arrangement of accessory genes, and the genes encoding the two enzymes are located
at least 15 kb apart on the chromosome. Both hydrogenases are
associated with the photosynthetic membrane. A stable and an
unstable hydrogenase activity can be detected in cells grown under nitrogen-fixing conditions; the latter activity is missing in
cells supplied with ammonia as the nitrogen source. The apparently constitutive and stable activity corresponds to hydrogenase 1, coded by
hydSL, and the inducible and unstable second hydrogenase may be the product of the hup gene cluster.
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Unusual Organization of the Genes Coding for HydSL, the Stable
[NiFe]Hydrogenase in the Photosynthetic Bacterium
Thiocapsa roseopersicina BBS
*
Corresponding author. Mailing address: Institute of
Biophysics, Biological Research Center, Hungarian Academy of Sciences, H-6701 Szeged, P.O. Box 521, Hungary. Phone: (36 62) 432 232. Fax: (36 62) 433 133. E-mail: kornel{at}szbk.u-szeged.hu.
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