Functional characterization of Xenopus laevis p53: evidence of temperature-sensitive transactivation but not of repression.

We have investigated the effect of Xenopus laevis p53 (Xp53) on transcription from a variety of promoters which are regulated by mouse p53 using a chloramphenicol acetyltransferase reporter system. Although Xp53 transactivated promoters that are up-regulated by mouse p53, it was unable to cause repression. This ability to transactivate gene expression was dependent on a temperature of 32 degrees C, and activity was lost at 37 degrees C. Temperature-sensitive transactivation was correlated with temperature-dependent binding of Xp53 to the adenovirus E1B58K protein. Despite the marked loss of transcriptional activation and binding to E1B58K at 37 degrees C, Xp53 was still capable of binding simian virus 40 large T antigen and inhibiting simian virus 40 origin-dependent DNA replication. These data show that Xp53 is temperature sensitive for N-terminal activities and suggest that the transactivation and repression "domains" of p53 are distinct.