DNA Polymerases of Tetrahymena pyriformis. II. Does an N-Ethylmaleimide-Resistant Polymerase Exist in Tetrahymena?

抄録

We investigated the relation between two N-ethylmaleimide (NEM)-sensitive DNA polymerases (designated as pol A and pol B in the preceding paper) and an NEM-resistant DNA polymerase (Furukawa et al. (1979) Nucl. Acids. Res. 7, 2387-2395) of Tetrahymena pyriformis with respect to changes in activity during cell growth and to chromatographic properties. Pol A activity per culture increased in accordance with the increase in cell number during the log phase but decreased during the stationary phase. Pol B and NEM-resistant polymerase activities per culture also increased during the log phase and the increases continued even in the stationary phase. All the changes were protein synthesis-dependent, since the changes were inhibited by treating the cells with cycloheximide. The changes of pol B and NEM-resistant polymerase activities during cell growth were always parallel and the ratio of the two enzymatic activities (NEM-resistant polymerase activity/pol B activity) remained constant with a value of about 0.03. This was also the case for cycloheximide-treated cultures. Furthermore, the enzymatic activities could not be separated by successive column chromatographies on phosphocellulose, DEAF-Sephadex A-25 and thiol-Sepharose. In these chromatographies, the elution profiles of the two activities coincided with each other and the activity ratio kept a constant value of about 0.03.
From these results, it is likely that the apparent NEM-resistant activity we measured corresponds to the remaining activity of pol B under NEM inhibition; in other words, no NEM-resistant polymerase really exists in Tetrahymena.