Sort the following events to reflect the normal order in which they occur in G-protein-coupled receptor signaling leading to transcription of genes with cAMP response elements (CRE). Your answer would be a four-letter string composed of numbers 1 to 4 only, e. g. 1-2-3-4.

(1) Phosphorylation of CREB (CRE-binding protein) by PKA;
(2) Activation of PKA;
(3) The catalytic subunits of PKA enter the nucleus;
(4) Activation of adenylyl cyclase;"