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squalene synthase HpnC This family of genes are members of a superfamily (pfam00494) of phytoene and squalene synthases which catalyze the head-t0-head condensation of polyisoprene pyrophosphates. The genes of this family are often found in the same genetic locus with squalene-hopene cyclase genes, and are never associated with genes for the metabolism of phytoene. In the organisms Zymomonas mobilis and Bradyrhizobium japonicum these genes have been characterized as squalene synthases (farnesyl-pyrophosphate ligases). Often, these genes appear in tandem with the HpnD gene which appears to have resulted from an ancient gene duplication event. Presumably these proteins form a heteromeric complex, but this has not yet been experimentally demonstrated.
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