Proteins in this family are now designated CbbX. Some previously were CfxQ (carbon fixation Q). Its gene is often found immmediately downstream of the Rubisco large and small chain genes, and it is suggested to be necessary for Rubisco expression. CbbX has been shown to be necessary for photoautotrophic growth. The Cfx genes in <taxon tax_id="106590">Ralstonia eutropha</taxon> (Alcaligenes eutrophus) encode a number of Calvin cycle enzymes [<cite idref="PUB00002204"/>]. The observed sizes of two of the gene products, CfxX and CfxY,are 35 kDa and 27 kDa respectively [<cite idref="PUB00002204"/>]. No functions could be assigned toCfxX and CfxY. These proteins show a high degree of similarity to the<taxon tax_id="1423">Bacillus subtilis</taxon> stage V sporulation protein K [<cite idref="PUB00003809"/>].