Ubiquitin ligase wwp-1 and ubiquitin conjugating enzyme ubc-18 are identified in nematodes as mediators of dietary restriction induced longevity and therefore as targets for modulation of lifespan in animals. Methods of screening for compounds that modulate longevity by assaying wwp-1 ubiquitination pathway parameters are provided, as are related systems. In addition, methods of using wwp-1 and/or ubc-18 to modulate longevity or delay onset of age-related diseases are described.