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DNA polymerases and SOS mutagenesis: can one reconcile the biochemical and genetic data?
1MRC Cell Mutation Unit, University of Sussex, Falmer, Brighton, BN1 9RR, UK. b.a.bridges@sussex.ac.uk
Abstract:
Until recently, it had been concluded from genetic evidence that DNA polymerase III (Pol III, the main replicative polymerase in E. coli) was also responsible for mutagenic translesion synthesis on damaged templates, albeit under the influence of inducible proteins UmuD' and UmuC. Now it appears that these proteins themselves have polymerase activity (and are now known as Pol V) and can carry out translesion synthesis in vitro in the absence of Pol III. Here I discuss the apparent contradictions between genetics and biochemistry with regard to the role of Pol III in translesion synthesis. Does Pol V interact with Pol III and constitute an alternative component of the replication factory (replisome)? Where do the other three known polymerases fit in? What devices does the cell have to ensure that the "right" polymerase is used in a given situation? The debate about the role of Pol III in translesion synthesis reveals a deeper divide between models that interpret everything in terms of mass action effects and those that embrace a replisome held together by protein-protein interactions and located as a structural entity within the cell.
Insights
DNA polymerase V (Pol V) performs mutagenic translesion synthesis, challenging the previous understanding of DNA polymerase III (Pol III) involvement. This discovery redefines the roles of polymerases in DNA repair and replication.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- Genetic evidence previously implicated DNA polymerase III (Pol III) in mutagenic translesion synthesis (TLS) in E. coli, under the control of UmuD' and UmuC proteins.
- Recent findings reveal that UmuD' and UmuC possess polymerase activity, now identified as Pol V, capable of TLS independently of Pol III.
Purpose of the Study:
- To reconcile apparent contradictions between genetic and biochemical data regarding Pol III's role in TLS.
- To explore the interaction between Pol V and Pol III within the replisome.
- To elucidate the roles of other polymerases and cellular mechanisms ensuring correct polymerase selection during DNA repair.
Main Methods:
- Review and discussion of existing genetic and biochemical evidence.
- Analysis of in vitro translesion synthesis assays.
- Theoretical modeling of replisome dynamics and polymerase interactions.
Main Results:
- Pol V can perform TLS in vitro without Pol III, directly contradicting earlier genetic interpretations.
- The precise interaction of Pol V with Pol III and its integration into the replisome remain under investigation.
- The cellular machinery for selecting the appropriate polymerase for specific DNA repair tasks is complex and not fully understood.
Conclusions:
- The discovery of Pol V's intrinsic TLS activity necessitates a re-evaluation of the established roles of DNA polymerases in E. coli.
- The findings highlight a fundamental debate between mass action models and structural replisome models for DNA replication and repair.
- Further research is required to fully integrate Pol V into the current understanding of the replisome and DNA damage tolerance pathways.