Cloning an Aspergillus nidulans developmental gene by transformation.

We have developed a transformation system for Aspergillus nidulans giving a frequency of transformation high enough to screen a gene bank from which we were able to isolate and clone the A. nidulans developmental gene brlA by visual selection. The vector contains the selective marker argB+, and with it a frequency of transformation of 500 stable transformants/micrograms plasmid DNA can regularly be achieved. The evidence suggests that transformation is by integration but spontaneous excision of integrated plasmids is apparently frequent enough to allow the recovery of transforming plasmids in Escherichia coli.     

Aspergillus nidulans stcP encodes an O-methyltransferase that is required for sterigmatocystin biosynthesis.

The Aspergillus nidulans stcP gene was previously identified as a transcribed region associated with a cluster of genes proposed to be involved in sterigmatocystin biosynthesis (D. W. Brown, J.-H. Yu, H. S. Kelkar, M. Fernandes, T. C. Nesbitt, N. P. Keller, T. H. Adams, and T. J. Leonard, Proc. Natl. Acad. Sci. USA 93:1418-1422, 1996). stcP was predicted to encode a methyltransferase responsible for conversion of demethylsterig-matocystin to sterigmatocystin. Here we demonstrate that disruption of stcP in A. nidulans results in strains that accumulate demethylsterigmatocystin.     

Gene control of developmental competence in Aspergillus nidulans

Conidia of Aspergillus nidulans placed in liquid nutrient medium germinate to produce hyphae that grow for a day or more as undifferentiated colonies. After 20 hr of growth, but not before, such colonies become responsive to induction and develop conidia-bearing structures (conidiophores) after being placed onto the surface of media-saturated membrane filters. Thus the time at which these colonies become developmentally competent is 20 hr. A mutant has been isolated which is indistinguishable from the wild-type strain except that it becomes competent to be induced 2 hr before the wild-type strain. At least one gene controlling competence has been characterized as a chromosomal allele. We have therefore been able to measure the time at which a growing colony becomes developmentally competent, and have shown that competence is under genetic control.