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

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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. TsAmaR‐1 is a TS for growth mutant of CHO cells with a Ts‐ and α‐amanitin‐resistant (AmaR) RNA polymerase II activity. Hybrid TsAmaR‐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 AmaR derivatives of TsAF8 were isolated. Each contained only AmaR 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 AmaR 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.