Other research projects are aimed at exploring the regulatory role of different nucleotides such ppGpp and pppGpp that are both thought to act as second messengers in many complex cellular responses to nutritional stress (Mechold et al., 2013), or of 3’-5’phosphoadenosine phosphate (pAp), a by-product of sulfur and lipid metabolism. We recently identified the Poly(ADP-ribose) Polymerase 1 (PARP-1), a key enzyme in the detection of DNA single strand breaks as a novel target of pAp (Toledano et al., 2012). We are also interested in the Exoenzyme Y (ExoY) virulence factor from Pseudomonas aeruginosa, a pathogen causing nosocomial infections in human. ExoY is a bacterial nucleotidyl cyclase that is injected by a type III secretion system into host cells where it is activated by an eukaryotic cofactor that we recently identified. ExoY produces a variety of cyclic nucleotides, cAMP, cGMP, cUMP in the infected host cells (Beckert et al. 2014). Their precise contributions to the pathogenicity of P. aeruginosa, remain to be clarified.