A trypsin-like proteinase appearing at 17 h and 17 min in the cell cycle time of HeLa cells correlates with the onset of DNA synthesis.

A trypsin-like proteinase appearing sharply at 17 h 17 min (17:17) in the cell cycle time of the synchronized and growing HeLa cells correlates with the onset of DNA synthesis, and the inhibition of the proteinase activity by trans-4-guanidinomethylcyclohexanecarboxylic acid 4-tert-butylphenyl ester (GMCHA-OPhBut) results in a 3 h retardation of the onset of the DNA synthesis. The proteinase activity is cell density dependent and completely inhibited by 100 microM GMCHA-OPhBut. The proteinase was named HeLa tryptase 17:17. The fact that the DNA synthesis occurred after the 3 h retardation in the presence of GMCHA-OPhBut strongly suggests the involvement of the alternative trigger for DNA synthesis in HeLa cells.