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Mouse p53 blocks SV40 DNA replication in vitro and downregulates T antigen DNA helicase activity
H W Stürzbecher1, R Brain, T Maimets
1Cell Proliferation Laboratory, Marie Curie Research Institute, Oxted, Surrey, UK.
Abstract:
Immunopurified mouse p53 proteins were used to gain experimental access to the mechanisms underlying nonprimate p53 directed suppression of SV40 origin directed DNA replication in vivo. In replication competent HeLa cell extracts containing exogenous T antigen, mouse p53 blocks T antigen dependent DNA synthesis as in vivo. However, in transcription competent HeLa extracts, mouse p53 has no effect either on overall transcription or on the ability of immunopurified T antigen to downregulate SV40 early transcription. We show that although mouse p53 has no significant effect on T antigen encoded activities such as ATPase and DNA binding, helicase activity is somewhat reduced suggesting that the in vivo suppression by mouse p53 of SV40 replication may be due, at least in part, to direct modulation of T antigen function.
Insights
Mouse p53 protein suppresses simian virus 40 (SV40) DNA replication by directly inhibiting T-antigen helicase activity. This p53 function occurs in vivo and in cell extracts, impacting DNA synthesis but not transcription.
Area of Science:
- Molecular Biology
- Virology
- Biochemistry
Background:
- The tumor suppressor protein p53 plays a critical role in cellular processes, including DNA replication and transcription.
- Simian virus 40 (SV40) replication is a well-studied model system involving the viral T-antigen.
- Understanding the interaction between p53 and viral replication machinery is crucial for deciphering cellular defense mechanisms.
Purpose of the Study:
- To investigate the mechanism by which non-primate p53 suppresses SV40 DNA replication.
- To determine if mouse p53 affects T-antigen's DNA replication or transcription functions.
Main Methods:
- Utilized immunopurified mouse p53 proteins in HeLa cell extracts.
- Assessed the impact of mouse p53 on T-antigen dependent DNA synthesis and SV40 early transcription.
- Evaluated T-antigen's ATPase, DNA binding, and helicase activities in the presence of mouse p53.
Main Results:
- Mouse p53 inhibited T-antigen dependent DNA synthesis in replication-competent HeLa cell extracts.
- Mouse p53 did not affect SV40 early transcription or T-antigen's ability to downregulate it.
- Mouse p53 showed no significant impact on T-antigen's ATPase and DNA binding activities but moderately reduced helicase activity.
Conclusions:
- Mouse p53 directly modulates T-antigen function, specifically reducing its helicase activity.
- This modulation of T-antigen helicase activity is a key mechanism for the in vivo suppression of SV40 replication by mouse p53.