Defective RNA polymerase II in the G1 specific temperature sensitive hamster cell mutant TsAF8

Abstract

TsAF8 is a temperature-sensitive (TS) mutant of BHK21 cells that arrests at nonpermissive temperatures in the mid-G₁ phase of the cell cycle. TsAma^R-1 is a TS for growth mutant of CHO cells with a Ts- and α-amanitin-resistant (Ama^R) RNA polymerase II activity. Hybrid TsAma^R-1 x TsAF8 cell lines were constructed at permissive temperatures. Such hybrid cells did not grow at nonpermissive temperatures; the two TS mutations did not complement. Two different Ama^R derivatives of TsAF8 were isolated. Each contained only Ama^R polymerase II activity, indicating that this RNA polymerase II gene locus in TsAF8 is functionally hemizygous, as would be expected for a locus in which the recessive TsAF8 mutation had occurred. One of these Ama^R isolates of TsAF8 had a partially reverted TS⁺ phenotype. Taken together these results suggest that the TS mutation in TsAF8 is in RNA polymerase II.