obsolete regulation of S phase of mitotic cell cycle true This term was made obsolete as part of the cell cycle overhaul. This is because it was decided that cell cycle phases are intervals and so cannot be regulated, rather it is the transitions between the phases that are regulated. regulation of S-phase of mitotic cell cycle OBSOLETE. A cell cycle process that modulates the frequency, rate or extent of the progression through the S phase of the mitotic cell cycle. GO:0007090 regulation of S phase of mitotic cell cycle biological_process mitotic cell cycle phase transition