Synthesis and degradation of microtubule protein in synchronized Chinese hamster cells.

Synthesis, degradation, and colchicine-binding characteristics of the microtubule protein were assayed in the cell cycle of two Chinese hamster lines. Levels of microtubule protein in the cell cycle were determined by electrophoresis of purified iodinated microtubule protein together with tritium-labeled whole cell lysates. Synthesis occurred almost exclusively in the G2 phase of the cloned aneuploid V79 line, whereas in the diploid Don line, considerable microtubule protein was synthesized in mid S phase as well as G2. In both Don and V79 cells, colchicine-binding activity displayed a pattern which was in agreement with the changing levels of microtubule protein determined with polyacrylamide gels. Degradation of the protein appeared to be intermittent. Microtubule protein synthesized in G2 phase survived into the ensuing Gl phase but was catabolized rapidly and concomitantly with initiation of DNA replication. The results show an intracyclic rhythm in microtubule synthesis and colchicine-binding activity and give support to the idea that oscillatory behavior of proteins is a common characteristic of the mammalian cell cycle.