Einfluß von Transkriptionsinhibitoren auf die Derepression der Riboflavinsynthase in der Hefe Torulopsis candida

Summary The action of actinomycin D on growth, nucleic acid and protein syntheses as well as on derepression of riboflavin synthase (EC 2.5.1.9) was followed in wild-type cells of the flavinogenic yeast, Torulopsis candida , as well as in an actinomycin D-sensitive mutant MST-2. In the wild-type strain growth and the incorporation of [2 -14 C]-guanine into nucleic acids were only slightly inhibited by the transcription inhibitor, whereas in the actinomycin D-sensitive mutant MST-2 growth cessation was at about 21μg actinomycin D per ml culture solution. Under these circumstances the incorporation of [2 -14 C]-guanine into nucleic acids was strongly reduced, whereas the incorporation of [ 14 C]-leucine into protein was unaffected. In the presence of α,α′-dipyridyl (an iron-chelating agent) the terminal enzyme of the riboflavin biosynthetic path, riboflavin synthase, is strongly derepressed in accordance with a high rate of riboflavin overproduction. Actinomycin D significantly inhibited riboflavin synthase of the mutant strain treated with α,α′-dipyridyl to trap iron. In wild-type cells of T. candida 2 other inhibitors, rubomycin and acriflavin, exerted the similar inhibitory effect as actinomycin D. It is suggested that iron which strongly represses riboflavin oversynthesis in flavinogenic yeasts is operative at the level of transcription.