Poly(ADP-ribose) synthesized after DNA damage is only present transiently and is rapidly degraded by poly(ADP-ribose) glycohydrolase (By similarity). Involved in establishing period length of the circadian oscillator. May regulate post-translational poly(ADP-ribosyl)ation of an oscillator component. [(1''->2')-ADP-alpha-D-ribose](n) + H2O = [(1''->2')-ADP-alpha-D-ribose](n-1) + ADP-D-ribose A number of isoforms are produced. According to EST sequences. Belongs to the poly(ADP-ribose) glycohydrolase family.