Northern blot analysis showing the expression of the chy and β-actin (control) genes in T7-36 and TAPL-4 strains. Total RNA was extracted at 36 and 48 h from cultures grown in MDFA3 medium either supplemented or not supplemented with 10 g/L casein. Analysis of the chy gene transcripts was performed using the 736-bp Stu I-Kpn I probe that is internal to the chy gene. For the analysis of the β-actin mRNA, the 834-bp Nco I-Kpn I fragment of the A. nidulans β-actin gene was used as probe. Note that similar expression levels are provided with and without casein.