The Phycomyces blakesleeanus wild-type is yellow, because it accumulates b-carotene as the main carotenoid. A new carotenoid mutant of this fungus (A486) was isolated, after treatment with ethyl methane sulfonate (EMS), showing a whitish coloration. It accumulates large amounts of phytoene, small quantities of phyto¯uene, f-carotene and neurosporene, in decreasing amounts, and traces of b-carotene. This phenotype indicates that it carries a leaky mutation a ecting the enzyme phytoene dehydrogenase (EC ), which is speci®ed by the gene carB
