Organization of phosphoribulokinase and ribulose bisphosphate carboxylase/oxygenase genes in Rhodopseudomonas (Rhodobacter) sphaeroides.

A heterologous phosphoribulokinase (PRK) gene probe was used to analyze two recombinant plasmids isolated from a Rhodopseudomonas (Rhodobacter) sphaeroides gene library. These plasmids were previously shown to carry the genes for form I and form II ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBPC/O). Southern blot hybridization analysis indicated that there were two PRK genes linked to the RuBPC/O coding sequences. Restriction mapping showed the arrangement of the duplicate sets of PRK and RuBPC/O to be distinct. Subcloning of the hybridizing PRK sequences downstream of the lac promoter of pUC8 allowed expression of the two PRK enzymes in Escherichia coli. Analysis of the purified proteins by sodium dodecyl sulfate-slab gel electrophoresis revealed polypeptides with molecular weights of 32,000 and 34,000 corresponding to the form I and form II PRKs, respectively. Preliminary experiments on sensitivity to NADH regulation suggested that the two PRK enzymes differ in catalytic properties.