Maximum activity of recombinant ribulose 1,5-bisphosphate carboxylase/oxygenase of Anabaena sp. strain CA requires the product of the rbcX gene.

Filamentous cyanobacteria of the genus Anabaena contain a unique open reading frame, rbcX, which is juxtaposed and cotranscribed with the genes (rbcL and rbcS) encoding form I ribulose 1,5-bisphosphate carboxylase/oxygenase (RubisCO). Plasmid constructions containing the genes from Anabaena sp. strain CA were prepared, and expression studies in Escherichia coli indicated that the product of the rbcX gene mimicked the ability of chaperonin proteins to facilitate the proper folding of recombinant RubisCO proteins. The purified recombinant Anabaena sp. strain CA RubisCO, much like the RubisCO enzymes from other cyanobacteria, was shown not to undergo inhibition of activity during a time course experiment, and the properties of this chaperoned recombinant protein appear to be consistent with those of the enzyme isolated from the native organism.