S. Bedu et al., UPTAKE OF INORGANIC CARBON IN THE CYANOBACTERIUM SYNECHOCYSTIS PCC6803 - PHYSIOLOGICAL AND GENETIC-EVIDENCE FOR A HIGH-AFFINITY UPTAKE SYSTEM, Molecular microbiology, 18(3), 1995, pp. 559-568
Synechocystis PCC6803 displays two inorganic carbon-uptake processes,
a low-affinity one (apparent K-m:300-400 mu M) functional in cells gro
wn under standard or limiting inorganic carbon concentrations, and one
with a higher affinity (60 +/- 12 mu M), detected only in cells adapt
ed to limiting inorganic carbon conditions. A mutational and screening
procedure allowed the isolation of a mutant deficient in the high-aff
inity system, but only slightly impaired in its growth capacities. The
mutated genomic region revealed two open reading frames (ORFs), possi
bly belonging to an operonic structure. A clone in which the downstrea
m ORF, hatR (high-affinity transport), had been inactivated showed a p
henotype close to that of the original mutant. Inactivation of the oth
er ORF, hatA, yielded a clone unable to grow in limiting inorganic car
bon conditions. The deduced HatA protein showed no homology with any r
egistered protein. It possessed three hydrophobic domains, including a
putative signal peptide, Several hypotheses are considered as to its
role. The deduced HatR protein, which possessed the features character
istic of the response regulators of the two-component regulatory syste
ms ubiquitous in bacteria, might be a regulator controlling the activi
ty of the high-affinity transport process. It would belong to the subc
lass of these molecules lacking the DNA-binding domain.