Temporal expression of transcription and relative copy number of plasmid pSFB-1 in Scytalidium flavo-brunneum.

Wild-type cultures of Scytalidium flavo-brunneum produce a 15-azasterol antifungal agent and a reddish brown pigment as secondary metabolites. Spontaneous mutants of S. flavo-brunneum that had simultaneously lost the ability to produce the 15-azasterol and the pigment were transformed with plasmid pSFB-1, which was obtained from wild-type S. flavo-brunneum. Each transformant possessed the plasmid and coincidentally reacquired azasterol and pigment production. Regulation of transcription and relative plasmid copy number was determined as a function of the culture cycle of the organism. Twenty-five-fold amplification of the plasmid was observed in the fungus during the stationary phase. RNA transcripts of 0.9, 1.0, 1.5, 2.0, and 2.5 kilobases were expressed from the plasmid by the organism. While differences in the temporal regulation of the transcripts were seen, all except the 1.0-kilobase transcript increased in abundance on entry of the culture into the stationary phase of growth.