A single gene for lycopene cyclase, phytoene synthase, and regulation of carotene biosynthesis in Phycomyces

Previous complementation and mapping of mutations that change the usual yel low color of the Zygomycete Phycomyces blakesleeanus to white or red led to the definition of two structural genes for carotene biosynthesis, We have cloned one of these genes, carRA, by taking advantage of its close linkage to the other, card, responsible for phytoene dehydrogenase, The sequences o f the wild type and six mutants have been established, compared with sequen ces in other organisms, and correlated with the mutant phenotypes, The carR A and card coding sequences are separated by 1,381 untranslated nucleotides and are divergently transcribed. Gene carRA contains separate domains for two enzymes, lycopene cyclase and phytoene synthase, and regulates the over all activity of the pathway and its response to physical and chemical stimu li from the environment. The lycopene cyclase domain of carRA derived from a duplication of a gene from a common ancestor of fungi and Brevibacterium linens; the phytoene synthase domain is similar to the phytoene and squalen e synthases of many organisms; but the regulatory functions appear to be sp ecific to Phycomyces.