Molecular Cloning and Sequencing of an Allium macrostemon cDNA Probably Encoding Oxidosqualene Cyclase.

Plant oxidosqualene cyclase (OSC) is classified into two types depeneding on its catalytic mechanisms and products: cycloartenol synthase and triterpene synthase. A cDNA probably encoding OSC was cloned from bulbs of Allium macrostemon by RT-PCR. The cDNA contains a 2289-by open reading frame, encoding 762 amino acids. A higher degree of homology (73%) was found for the gene product with the known cycloartenol synthases than with the triterpene synthases (51-55%), indicating its most likely function as cycloartenol synthase. This is the first cloning example of a putative cDNA encoding OSC from a monocotyledonous plant.