Fig. 1. Regulation of the sulfate assimilation pathway in SCF^Met30 mutants. The strains were grown for eight generations in B medium with 0.2 mM dl-homocysteine as sulfur source, shifted to 37°C for 2 h and a repressing amount of l-methionine (1 mM) was then added. Total RNA was extracted at the indicated times after l-methionine addition, and expression of MET genes was determined by Northern blot analysis. The actin probe was used as a control of the amount of RNA loaded.