Strains and plasmids. A. niger wild-type strain N400 (CBS 120.49) was used for the construction of a genomic library in the lambda vector EMBL4 from Promega Biotech Inc, Madison, Wis (Frischauf et al. 1983). The pyrA- A. niger strain N593 (Goosen et al. 1987) was used for transformation, pCG3B~I (Gysler et al.
1990) contains the A. niger strain N756 peID gene, pGW613 (Goosen et al. 1987) contains the A. niger pyrA gene. All plasmids were propagated in E. coli MH1 (Goddard et al. 1983).