Hereâs an example of how a signal transduction pathway can turn on a gene in the cell nucleus. A signal binds to a G protein-coupled receptor, triggering a signal transduction pathway: a G protein is activated, which activates adenylyl cyclase, which converts ATP to cyclic AMP. The second messenger cyclic AMP triggers a phosphorylation cascade, activating a series of protein kinases. The last phosphorylated kinase enters the nucleus and activates a transcription factor, which stimulates transcription of a specific gene. The resulting mRNA then moves to the cytoplasm and directs the synthesis of a new protein.