obsolete regulation of S phase true regulation of progression through S phase biological_process regulation of S-phase GO:0033261 This term was made obsolete because cell cycle phases are intervals and so cannot be regulated as such, rather it is the transitions between the phases that are regulated. This term was often also used to annotate genes which should have been annotated to 'regulation of DNA replication', or one of its children. regulation of S phase OBSOLETE. A cell cycle process that modulates the rate or extent of the progression through the S phase of the cell cycle. cell cycle phase transition