Uptake of inorganic carbon in the cyanobacterium Synechocystis PCC6803: physiological and genetic evidence for a high-affinity uptake system.
Synechocystis PCC6803 displays two inorganic carbon-uptake processes, a low-affinity one (apparent Km: 300-400 microM) functional in cells grown under standard or limiting inorganic carbon concentrations, and one with a higher affinity (60 +/- 12 microM), detected only in cells adapted to limiting inorganic carbon conditions. A mutational and screening procedure allowed the isolation of a mutant deficient in the high-affinity system, but only slightly impaired in its growth capacities. The mutated genomic region revealed two open reading frames (ORFs), possibly belonging to an operonic structure. A clone in which the downstream ORF, hatR (high-affinity transport), had been inactivated showed a phenotype close to that of the original mutant. Inactivation of the other ORF, hatA, yielded a clone unable to grow in limiting inorganic carbon conditions. The deduced HatA protein showed no homology with any registered 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 characteristic of the response regulators of the two-component regulatory systems ubiquitous in bacteria, might be a regulator controlling the activity of the high-affinity transport process. It would belong to the subclass of these molecules lacking the DNA-binding domain.
Bëdu
S
S
Laboratoire de Chimie Bacterienne, CNRS, Marseille, France.
Pozuelos
P
P
Cami
B
B
Joset
F
F
D000595:Amino Acid Sequence; D001483:Base Sequence; D002244:Carbon / Q000378:metabolism*; D000458:Cyanobacteria / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D007700:Kinetics; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D009154:Mutation; D016366:Open Reading Frames; D010641:Phenotype; D015183:Restriction Mapping; D016415:Sequence Alignment
D002244:Carbon