Optimal activation of transcription of the GAL genes in yeast requires the function of two proteins: Gal4p and Gal11p. Elimination of either protein decreases activation of the GAL promoters. However, inactivation of Gal11p has the additional and dramatic effect of cell lethality. Why might elimination of Gal11p have a greater effect than elimination of Gal4p

Gal4p is a transcription factor that targets specific GAL genes, while Gal11p is a core component of the Mediator complex that plays regulatory roles in the expression of many different genes (class II genes) in eukaryotic organisms

Explanation:

The Gal4 transcription factor is one of the most widely studied eukaryotic transcriptional activators capable of activating the expression of galactose-induced genes. Gal4 is well-known to target specific enzymes involved in galactose metabolism: GAL1, GAL7, and GAL10. On the other hand, Gal11p is a key subunit of the evolutionary conserved Mediator complex that binds to the RNA polymerase II (RNAP II) in order to regulate the transcription of class II genes (i.e., genes transcribed by RNAP II).