(A) The HOM3 and THR1 genes were placed under the control of the PCTR4-1 promoter by inserting the NAT1-PCTR4-1 construct immediately upstream of the predicted ORF, as shown in the diagram. (B) Southern hybridization analysis confirming correct positioning of the NAT1-PCTR4-1 construct in strains H99-73 (PCTR4-1-THR1) and H99-76 (PCTR4-1-HOM3). Genomic DNA from strains H99 (wildtype), H99-73 and H99-76 was digested with the restriction enzymes indicated, and blots were hybridized as indicated with a HOM3 or THR1 DNA probe, amplified using primer pairs JO414+JO413 and JO506+JO362, respectively.