[Effect of temperature on the transcription of T3 DNA b y T3-specific RNA polymerase in cell-free extracts of Escherichia coli CRT266].

Cell free extracts were prepared from E. coli CRT266 9 min after infection with T3 phages. RNA synthesis in these extracts is almost entirely due to T3 RNA polymerase. The inactivation of T3 RNA polymerase in these extracts proceeds rapidly at 42 degrees C. 90% of the activity is lost within 10 min at this temperature. Under conditions where the formation of a stable initiation complex with T3 DNA is possible, i.e., in the presence of GPT, APT, and UTP the T3 RNA polymerase becomes protected against heat inactivation losing only )0% of its activity during an exposure to 42 degrees C for 10 min. Studies on the time course of RNA synthesis have shown that reinitiation is still possible at 37 degrees C and 42 degrees C. At 44 degrees C, however, RNA synthesis stops abruptly after 3 min indicating that reinitiation does no longer take place. The elongation of already initiated T3 RNA chains is rather resistant to heat. At 44 degrees C the same elongation rates are observed as at 37 degrees C and 42 degrees C, respectively.