Fig. 2. Southern blot analysis of transformants containing carB exogenous sequences. Total DNA (0.75 µg) from the wild-type strain R7B (WT) and albino and wild-type transformants was digested with EcoRI and XhoI, and hybridized with a 1.8 kb cDNA fragment of carB. (A) Wild-type (T1-T3) and albino (T4-T5) transformants obtained with plasmid pMAT647. (B) Albino (T6-T9) and wild-type (T10-T13) transformants obtained with plasmid pMAT754. The EcoRI–XhoI digestion generates a 3.6 or 3.7 kb fragment from plasmids pMAT754 and pMAT647, respectively, which include the complete carB insert. The 4.5 kb fragment corresponds to the endogenous carB gene. Densitometric analysis of the hybridizing bands was used to calculate the copy number of carB exogenous sequences per nucleus.