Resolution of chromosomes III and VI of Aspergillus nidulans by pulsed-field gel electrophoresis shows that the penicillin biosynthetic pathway genes pcbAB, pcbC, and penDE are clustered on chromosome VI (3.0 megabases).

An improved electrophoretic molecular karyotype of Aspergillus nidulans ATCC 28901 has been obtained by contour-clamped electric field gel electrophoresis, which separates seven chromosomal bands and allows resolution of chromosomes III and VI. The three genes of the penicillin biosynthetic pathway, pcbAB, pcbC, and penDE, encoding alpha-aminoadipyl-cysteinyl-valine synthetase, isopenicillin N synthase, and isopenicillin N acyltransferase, respectively, are clustered together on a chromosome of 3.0 Mg, corresponding to linkage group VI, whereas the argB gene was located on a chromosome of 3.4 Mb, corresponding to linkage group III. Three other strains of A. nidulans contained a modified chromosome III of about 3.1 Mb that overlaps with chromosome VI, forming a doublet. Resolution of chromosomes III and VI in strain ATCC 28901 allowed unequivocal mapping of the penicillin gene cluster on chromosome VI of A. nidulans.