Genetic analysis of Aspergillus nidulans AmdS+ transformants

To correlate the genetic background of the Aspergillus nidulans amdS deletion strain MH1277 with the integrational behaviour of transforming vectors, classical genetic methods were used to construct AmdS- strains in which whole chromosomes had been exchanged with those of a master strain. Progeny strains were transformed to the AmdS+ phenotype with vector p3SR2. From Southern analysis it was concluded that transformants from all constructions contained tandemly repeated, multiple copy inserts of vector DNA as found for MH1277-derived AmdS+ transformants. AmdS+ transformants of MH1277 were analysed genetically to prove that the transformant phenotype is genome linked and that transformation by integration can take place on various chromosomes. In one case the AmdS+ property showed linkage to both chromosomes II and IV, due to a chromosomal translocation. Sexual analysis of two transformants with AmdS+ insertions on the same chromosome revealed a considerable instability of the AmdS+ phenotype in one of the strains upon selfing. Due to this instability no decisive answer could be given for the degree of linkage between the AmdS+ insertions in these transformants.