text_1: Free histones are degraded by a Rad53-dependent mechanism once DNA has been replicated.
text_2: We have also identified the ubiquitin conjugating enzymes (E2) Ubc4 and Ubc5, as well as the ubiquitin ligase (E3) Tom1 (temperature dependent organization in mitotic nucleus 1), as enzymes involved in the ubiquitylation of excess histones.