1. Grow cells to subconfluent (mid-log phase).
2. Add thymidine to a final concentration of 2 mM for 16-24 hours
(one cell cycle).
3. Wash cells with PBS three times and re-feed with fresh grow
4. Incubate for 10 hours before adding thymidine to a final concentration
of 2 mM.
5. Incubate for 14-22 hours.
6. Repeat step 3. This will be time 0.