Temperature-sensitive RNA polymerase of a mammalian cell mutant.

In our attempts to characterize a temperature-sensitive mutant (ts-2) of monkey kidney cell line BSC-i, we have provided evidence to show that the mutant was defective in the synthesis or processing of rRNA (45, 28 and 18 s) molecules at 39-5 °C and there was indication that the nucleolar RNA polymerase (I) or some factor associated with its functional activity was thermolabile at the restricted temperature of 39-5 °C. The enzyme in the wild type cell line was, however, stable at this temperature. Though conclusive evidence to implicate RNA polymerase (I) was not obtained in these experiments, temperature-sensitivity tests with crude enzyme extracts of the RNA polymerase in ts-2 showed that it contained a temperature-sensitive factor which was either degraded rapidly or failed to be eluted out of the DEAE-Sephadex column. This temperature-sensitive factor was not affected by a-amanitin.