S. Elsen et al., THE HUPTUV OPERON IS INVOLVED IN NEGATIVE CONTROL OF HYDROGENASE SYNTHESIS IN RHODOBACTER-CAPSULATUS, Journal of bacteriology, 178(17), 1996, pp. 5174-5181
The hupT, hupU, and hupV genes, which are located upstream from the hu
pSLC and hypF genes in the chromosome of Rhodobacter capsulatus, form
the hupTUV operon expressed from the hupT promoter. The hupU and hupV
genes, previously thought to belong to a single open reading frame, en
code HupU, of 34.5 kDa (332 amino acids), and HupV, of 50.4 kDa (476 a
mino acids) which are greater than or equal to 50% identical to the ho
mologous Bradyrhizobium japonicum HupU and HupV proteins and Rhodobact
er sphaeroides HupU1 and HupU2 proteins, respectively; they also have
20 and 29% similarity with the small subunit (HupS) and the large subu
nit (HupL), respectively, of R. capsulatus [NiFe]hydrogenase. HupU lac
ks the signal peptide of HupS and HupV lacks the C-terminal sequence o
f HupL, which are cleaved during hydrogenase processing. Inactivation
of hupV by insertional mutagenesis or of hupUV by in-frame deletion le
d to HupV(-) and Hup(UV)(-) mutants derepressed by hydrogenase synthes
is, particularly in the presence of oxygen. These mutants were complem
ented in trans by plasmid-borne hupTUV but not by hupT or by hupUV, ex
cept when expressed from the inducible fur promoter. Complementation o
f the HupV(-) and Hup(UV)(-) mutants brought about a decrease in hydro
genase activity up to 10-fold, to the level of the wild-type strain B1
0, indicating that HupU and HupV participate in negative regulation of
hydrogenase expression in concert with HupT, a sensor histidine kinas
e involved in the repression process. Plasmid-borne gene fusions used
to monitor hupTUV expression indicated that the operon is expressed at
a low level (50- to 100-fold lower than hupS).