ADP-ribosylation has been coupled to intracellular events associated with smooth muscle cell vasoreactivity, cytoskel-etal integrity and free radical damage. Additionally, there is evidence that ADP-ribosylation is required for smooth muscle cell proliferation. Our investigation employed selective inhibitors to establish thatmono-ADP-ribosylation and not poly(ADP-ribosyl)ation was necessary for the sti-mulationofDNAsynthesis bymitogens.

Endogenous mono-ADP-ribosylation in eukaryotes is involved in regulating protein synthesis, signal transduction, cytoskeletal integrity, and cell prolifer-ation, although few cellular ADP-ribosyltransferases have been identified. The sirtuins constitute a highly conserved family of protein deacetylases, and several family members have also been reported to perform protein ADP-ribosylation.