Constitutive expression of the yeast HEM1 gene is actually a composite of activation and repression.

@article{Keng1987ConstitutiveEO,
  title={Constitutive expression of the yeast HEM1 gene is actually a composite of activation and repression.},
  author={Teresa Keng and Leonard P. Guarente},
  journal={Proceedings of the National Academy of Sciences of the United States of America},
  year={1987},
  volume={84 24},
  pages={9113-7}
}
We show that HEM1 (encoding 5-aminolevulinate synthase) expression, while constitutive under all steady-state growth conditions tested, is activated by the HAP2-HAP3 global activation system that controls expression of apocytochromes. This finding creates a paradox because apocytochrome activation by HAP2-HAP3 is highly regulated, subject to induction by heme, and subject to further derepression by a shift from glucose medium to one containing a nonfermentable carbon source. We clarify this… CONTINUE READING