The cbbQ genes, located downstream of the form I and form II RubisCO genes, affect the activity of both RubisCOs.

Hydrogenovibrio marinus strain MH-110, an obligately lithoautotrophic hydrogen-oxidizing bacterium, possesses three sets of the genes for ribulose 1,5-bisphosphate carboxylase/oxygenase (RubisCO): namely, two form I type (cbbLS-1 and cbbLS-2) and one form II type (cbbM) enzymes. The cbbQ-m gene was located downstream of cbbM, and showed high similarity to other cbbQ genes and nirQ/norQ genes in denitrifying bacteria. Phylogenetic analysis of CbbQ and NirQ/NorQ indicated that CbbQ-m from Hv. marinus closely resembled CbbQ from Thiobacillus intermedius and Thiobacillus neapolitannus and less closely resembled NirQ and NorQ. The cbbQ-m gene has been shown to activate the form II RubisCO in E. coli cells, and the cbbQ-t from Hydrogenophilus thermoluteolus could also activate the form II RubisCO. Both cbbQ genes have also been shown to activate the form I RubisCO from Hp. thermoluteolus in E. coli cells. However, the activation levels of two form I RubisCOs from Hv. marinus were smaller than that of form I RubisCOs from Hp. thermoluteolus. Form II RubisCO activated by CbbQ-m (QM) was purified from E. coli cells. The result of the 8-anilino-1-naphthalenesulfonate binding assay and the circular dichroism spectra indicated that QM was conformationally different from Form II RubisCO that was not activated by CbbQ. Copyright 1999 Academic Press.