The rbcX gene product promotes the production and assembly of ribulose-1,5-bisphosphate carboxylase/oxygenase of Synechococcus sp. PCC7002 in Escherichia coli.

The operon encoding ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) in the cyanobacterium Synechococcus sp. PCC7002 contains three rbc genes, rbcL, rbcX and rbcS, in this order. Introduction of translational frameshift into the rbcX gene resulted in a significant decrease in the production of large (RbcL) and small (RbcS) subunits of the Rubisco protein in Synechococcus sp. PCC7002 and in Escherichia coli. To investigate the function of the rbcX gene product (RbcX), we constructed the expression plasmid for the rbcX gene and examined the effects of RbcX on the recombinant Rubisco production in Escherichia coli. The coexpression experiments revealed that RbcX had marked effects on the production of large and small subunits of Rubisco without any significant influence on the mRNA level of rbc genes and/or the post-translational assembly of the Rubisco protein. The present rbcX coexpression system provides a novel and useful method for investigating the Rubisco maturation pathway.