And the Pip Three itself is actually produced by the phosphorusotide three kinase. Now, in our discussion of EGF signaling, we actually did not examine these two secondary messengers, but these are in fact secondary messengers that stimulate the EGF signaling pathway. So calcium as well as cyclic adenosine monophosphate. Now, let's move on to property number three that all these four have in common. And that's the fact that all of these different pathways depend on the correct interaction between protein molecules and other molecules in that pathway. So within any signal transduction pathway, proteins interact with other molecules.