This family contains bacterial hydrogenase-1 expression proteins approximately 120 residues long. This includes the E. coli protein HyaE, and the homologous proteins HoxO of R. eutropha and HupG of R. leguminosarum. Deletion of the hoxO gene in R. eutropha led to complete loss of the uptake [NiFe] hydrogenase activity, suggesting that it has a critical role in hydrogenase assembly [1].

1: Assembly of Tat-dependent [NiFe] hydrogenases: identification of precursor-binding accessory proteins. Dubini A, Sargent F; FEBS Lett 2003;549:141-146. PMID:12914940