Role of adenylyl cyclase in signal transduction?

Answer 1

It is an enzyme that is first activated by G proteins within the cell to catalyse a second messenger cyclic AMP or (cAMP)

cAMP activates protein kinase A.
protein kinase A phosphorylates serine and threonine.

So adenylate cyclase is part of a cascade reaction in cellular transduction

Answer 2

is the protein that's usually embedded in the phospholipid bilayer. Once AC is triggered ADP is transformed in ATP, which then is turn turns on other pathways that's in the cell. One example is vision.
http://www.vivo.colostate.edu/hbooks/molecules/cyclase.html

Answer 3

Try these references.