Regulation of Carotene Biosynthesis in <em>Phycomyces</em> by Vitamin A and <em>β</em>-Ionone.

The presence of vitamin A in the medium results in a large increase in Β-carotene content in wild-type Phycomyces blakesleeanus; in carB mutants. which accumulate phytoene. and carR mutants. which accumulate lycopene, the presence of vitamin A results in an increase in these intermediates. In carA mutants. which usually form no carotenoids. vitamin A partially counteracts the mutational block and allows Β-carotene synthesis. Vitamin A is not itself converted to Β-carotene. Β-ionone. long known as a stimulator of carotenogenesis, can also counteract carA mutations. The effects of vitamin A and Β-ionone do not occur in the presence of the protein-synthesis inhibitor cycloheximide. Vitamin A and Β-ionone stimulate carotenogenesis through the normal pathway. probably by interaction with the carA gene product. [ABSTRACT FROM AUTHOR]