The Molecular History of Eukaryotic Life  Cyclic Nucleotides 


David Nelson  Dec. 13, 2000

	cAMP is found in all three domains of life: bacteria, archaea and eukarya.  In 
eukaryotes, it activates protein kinase A (PKA).  It is secreted as a signal by 
Dictyostelium and it binds to seven transmembrane receptors in this organism.  Bacteria 
use it to regulate gene expression in catabolite repression, where glucose can repress 
the synthesis of genes needed to metabolize other carbon sources.  The glucose signal 
activates a cAMP phosphodiesterase that decreases cAMP concentrations.  cAMP normally 
binds to a protein called CRP (cAMP receptor protein) or CAP (Catabolite gene-activator 
protein) and this protein binds to DNA and activates gene expression of an operon.  When 
the cAMP level drops, the CAP protein can no longer activate the genes and their 
transcription is reduced or stopped.  cAMP is one of the most ancient of regulatory 
signaling molecules.

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