What are the similarities between cAMP and cGMP?

There are various similarities between cAMP and cGMP. One similarity is that they are both types of cyclic nucleotides. They both act as second messengers in both ion-channel and hormone signaling in eukaryotes. Another similarity is that they both act as allosteric effector compounds of DNA-binding proteins in prokaryotes. cAMP and cGMP both have a wide range of protein-ligand interactions, and are able to activate protein kinases.