Gene cloning and transformation in the basidiomycete fungus Coprinus cinereus: Isolation and expression of the isocitrate lyase gene (acu-7)

Summary The cloned isocitrate lyase structural gene of Aspergillus nidulans (acuD) was shown to hybridize under reduced stringency conditions to unique sequences in genomic DNA digests of the basidiomycete fungus Coprinus cinereus. A gene library of C. cinereus was constructed in the lambda replacement vector L47 and screened for sequences hybridizing to the A. nidulans gene. A recombinant phage was isolated which contained the hybridizing sequence on a 5.6-kb BamHI fragment. This fragment was subcloned into pUC13 to give plasmid pHIONA1 and shown to contain a functional C. cinereus isocitrate lyase gene (acu-7) by transformation of an acu-7 mutant. Direct selection for Acu⁺ transformants was not possible because of the toxicity of the acetate selection medium. Acu⁺ transformants were obtained as cotransformants by transforming an acu-7 trp-1 double mutant, having mutations in both the isocitrate lyase and tryptophan synthetase structural genes, with a plasmid containing the trp-1 gene and either pHIONA1 or the original lambda clone. Up to 47.5% of the selected Trp⁺ transformants were cotransformed to Acu⁺. A physical analysis of 40 Acu⁺ transformants showed that the acu-7 gene had integrated at non-homologous and often multiple sites in the genome. Meiotic stability of the integrated gene was demonstrated by genetic crosses.