Changes in RNA polymerase II in a cell cycle‐specific temperature‐sensitive mutant of hamster cells

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Abstract
TsAF8 cells are a temperature‐sensitive mutant of BHK cells that arrest at the nonpermissive temperature in the G1 phase of the cell cycle. The activity of solubilized RNA polymerase II and its ability to bind [3H]‐γ‐amanitin decrease in tsAF8 cells at 40.6°, with a half‐life of ∼ 10 hr. No appreciable changes occur in these two parameters in tsAF8 cells at 34° or in BHK cells at either 34° or 40.6°. Protein synthesis is not appreciably affected for at least 24 hr after tsAF8 cells are shifted to 40.6°. These results indicate that in tsAF8 cells at the nonpermissive temperature, there is a defect in either the synthesis, the assembly, or the stability of RNA polymerase II, and that the loss of RNA polymerase II molecules is not due to widespread cellular damage.