Escape from X-Ray-Induced Arrest for Lens Cells Stimulated from Quiescence: Time Relationship to RNA, Protein, and DNA Synthesis

Quiescent cells of the central zone region of the rat lens epithelium were stimulated to enter the proliferation cycle by wounding. RNA synthesis and a corresponding increase in <tex-math>${\rm poly}({\rm A})^{+}/\text{total}$</tex-math> RNA reached a peak by Hour 4. Cells progressed into the <tex-math>${\rm G}_{1{\rm B}}$</tex-math> compartment by Hour 10. A rise in protein synthesis began at Hour 8, and onset of DNA synthesis occurred by Hour 14. The timing of cell cycle progression that allowed escape from a dose of X irradiation that completely inhibited DNA synthesis was investigated. A growth-arrest point was identified at Hour 9 where 10 Gy of X irradiation given before, but not after, completely inhibited earliest responding cells from entering DNA synthesis on schedule. Increased quantities of cells entered DNA synthesis on schedule as timing of the X irradiation was moved closer to the end of G₁. Based on time relationships, the rise in protein synthesis is correlated with the "sufficient" event for the escape.