Question

You are trying to work out the order in which two intracellular proteins of a newly-discovered signaling pathway function. These two proteins, Sony and Cher, are both kinases, and you know that they act sequentially in this pathway. When either kinase is completely inactivated, cells fail to respond to the extracellular signal. On the other hand, cells that contain a mutant form of Sony that is constitutively active respond even in the absence of the external ligand. Doubly-mutant cells that contain an inactive form of Cher and the constitutively active form of Sony also respond in the absence of the external ligand. In the normal pathway, does Sony activate Cher or does Cher activate Sony? Explain your reasoning

Answer 1

It seems that the constitutively active mutant form of the protein , Sony , works independently i.e. it is not controlled by the inactive form of the protein, Cher.

Normally, if either of the protein is inactive, the functioning of the signal pathway of the cell is disrupted.

But this changes when the protein , Sony, is mutated to a constitutively active form.

From of the above information, we can assume that the protein Sony is not controlled by Cher. It can function even if Cher is in a mutated active form. So, Sony activates Cher .