A genetically encoded, fluorescent indicator for cyclic AMP in living cells

Cyclic AMP controls several signalling cascades within cells, and changes i n the amounts of this second messenger have an essential role in many cellu lar events. Here we describe a new methodology for monitoring the fluctuati ons of cAMP in living cells, By tagging the cAMP effector protein kinase A with two suitable green fluorescent protein mutants, we have generated a pr obe in which the fluorescence resonance energy transfer between the two flu orescent moieties is dependent on the levels of cAMP, This new methodology opens the way to the elucidation of the biochemistry of cAMP in vivo.