Transformation of Aspergillus nidulans by using a trpC plasmid.

We constructed a chimeric plasmid carrying a complete copy of the trifunctional trpC gene from the Ascomycete fungus Aspergillus nidulans. This plasmid, designated pHY201, replicates in Escherichia coli, where it confers resistance to ampicillin and chloramphenicol and complements trpC mutants lacking phosphoribosylanthranilate isomerase activity. We used pHY201 to transform an A. nidulans trpC- strain to trpC+ at frequencies of greater than 20 stable transformants per microgram of DNA. Southern blot analysis of DNA from transformants showed that pHY201 DNA had integrated into the A. nidulans chromosomes in a majority of cases. Most of the integration events appeared to occur at the site of the trpC- allele of the recipient strain. In several instances, we succeeded in recovering pHY201, or derivatives thereof, from A. nidulans transformants by restriction endonuclease digestion of chromosomal DNA, ligation, and transformation of E. coli.