The s phase is discrete and is controlled by the circadian clock in the marine dinoflagellate Gonyaulax polyedra.

@article{Homma1989TheSP,
  title={The s phase is discrete and is controlled by the circadian clock in the marine dinoflagellate Gonyaulax polyedra.},
  author={Keiichi Homma and John Woodland Hastings},
  journal={Experimental cell research},
  year={1989},
  volume={182 2},
  pages={635-44}
}
Cloned cultures of the dinoflagellate Gonyaulax polyedra grown in a 12-h light-12-h dark cycle (LD 12:12) were synchronized to the beginning of G1 by a two sequential filtration technique. After the second filtration, with the cultures growing in LD 12:12, not many cells had divided after 1 day, but approximately half underwent cell division after 2 days. Flow cytometric measurements of the cells revealed that there is one unique S phase starting about 12 h prior to cell division and lasting… CONTINUE READING