PMID:15037066

Citation	Tanguy Le Gac, N, Delagoutte, E, Germain, M and Villani, G (2004) Inactivation of the 3'-5' exonuclease of the replicative T4 DNA polymerase allows translesion DNA synthesis at an abasic site. J. Mol. Biol. 336:1023-34
Abstract	Here, we have investigated the consequences of the loss of proof-reading exonuclease function on the ability of the replicative T4 DNA polymerase (gp43) to elongate past a single abasic site located on model DNA substrates. Our results show that wild-type T4 DNA polymerase stopped at the base preceding the lesion on two linear substrates having different sequences, whereas the gp43 D219A exonuclease-deficient mutant was capable of efficient bypass when replicating the same substrates. The structure of the DNA template did not influence the behavior of the exonuclease-proficient or deficient T4 DNA polymerases. In fact, when replicating a damaged "minicircle" DNA substrate constructed by circularizing one of the linear DNA, elongation by wild-type enzyme was still completely blocked by the abasic site, while the D219A mutant was capable of bypass. During DNA replication, the T4 DNA polymerase associates with accessory factors whose combined action increases the polymerase-binding capacity and processivity, and could modulate the behavior of the enzyme towards an abasic site. We thus performed experiments measuring the ability of wild-type and exonuclease-deficient T4 DNA polymerases, in conjunction with these replicative accessory proteins, to perform translesion DNA replication on linear or circular damaged DNA substrates. We found no evidence of either stimulation or inhibition of the bypass activities of the wild-type and exonuclease-deficient forms of T4 DNA polymerase following addition of the accessory factors, indicating that the presence or absence of the proof-reading activity is the major determinant in dictating translesion synthesis of an abasic site by T4 DNA polymerase.
Links	PubMed Online version:10.1016/j.jmb.2004.01.005
Keywords	Bacteriophage T4/enzymology; Bacteriophage T4/genetics; Base Sequence; DNA Damage; DNA Replication; DNA-Directed DNA Polymerase/genetics; DNA-Directed DNA Polymerase/metabolism; Exonucleases/genetics; Exonucleases/metabolism; Kinetics; Mutation, Missense; Viral Proteins/genetics; Viral Proteins/metabolism
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
BPT4:DPOL		GO:0008408: 3'-5' exonuclease activity	ECO:0000315:		F		Figure 4 and Figure 5 show that the mutant phenotype of T4 that is lacking exonuclease has altered DNA polymerase activity. The wild type T4 used the proof reading exonuclease to stop at lesions in the DNA, whereas the mutant phentotype DNA polymerase bypassed the lesions due to lack of exonuclease.	complete CACAO 11937

References

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