User:Nathan Harris/Tus: Difference between revisions
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==='''Tus-DnaB interactions'''=== | ==='''Tus-DnaB interactions'''=== | ||
Numerous studies support a model for replication termination resulting specifically from Tus-DnaB protein interactions. Experimentation in the field has demonstrated that the <scene name='User:Nathan_Harris/Tus/E49/1'>E49</scene> within the L1 loop of the non-permissive face of Tus is important in the formation of protein-protein interactions with DnaB. When this glutamic acid is exchanged for lysine (E49K), an increase in affinity for ''Ter'' and a decrease in affinity for DnaB result <ref name = "Henderson"> Henderson, T., Niles, A., Valjavec-Gratian, M. and Hill, T. (2001) Site-directed mutagenesis and phylogenetic comparisons of Escherichia coli Tus protein: DNA-protein interactions alone cannot account for Tus activity. Molecular Genetics and Genomics, 265 (6): 941-953.</ref><ref name = "Mulugu"> Mulugu, S., Potnis, A., Shamsuzzaman, T. J., Alexander, K. and Bastia, D. (2001) Mechanism of termination of DNA replication of Escherichia coli involves helicase-contrahelicase interaction. Proceedings of the National Academy of Science, USA, 98 (17): 9569-9574.</ref>. Despite the increased affinity for ''Ter'', this E49K mutatation results in a reduced capability of polar replication fork termination demonstrating the importance of Tus-DnaB interactions. | Numerous studies support a model for replication termination resulting specifically from Tus-DnaB protein interactions. Experimentation in the field has demonstrated that the <scene name='User:Nathan_Harris/Tus/E49/1'>E49</scene> within the L1 loop of the non-permissive face of Tus is important in the formation of protein-protein interactions with DnaB. When this glutamic acid is exchanged for lysine (E49K), an increase in affinity for ''Ter'' and a decrease in affinity for DnaB result <ref name = "Henderson"> Henderson, T., Niles, A., Valjavec-Gratian, M. and Hill, T. (2001) Site-directed mutagenesis and phylogenetic comparisons of Escherichia coli Tus protein: DNA-protein interactions alone cannot account for Tus activity. Molecular Genetics and Genomics, 265 (6): 941-953.</ref><ref name = "Mulugu"> Mulugu, S., Potnis, A., Shamsuzzaman, T. J., Alexander, K. and Bastia, D. (2001) Mechanism of termination of DNA replication of Escherichia coli involves helicase-contrahelicase interaction. Proceedings of the National Academy of Science, USA, 98 (17): 9569-9574.</ref>. Despite the increased affinity for ''Ter'', this E49K mutatation results in a reduced capability of polar replication fork termination demonstrating the importance of Tus-DnaB interactions. | ||
In further confirmation of this helicase specific mechanism, the engineering of intra-strand covalent crosslinks introduced immediately upstream of the C6 of ''Ter'' prevent DnaB helicase from unwinding the C6. Despite this inability to unwind and from a locked complex with ''Tus'', polar fork termination is still permitted indicating that the formation of a locked complex is unnecessary for replication termination. | In further confirmation of this helicase specific mechanism, the engineering of intra-strand covalent crosslinks introduced immediately upstream of the C6 of ''Ter'' prevent DnaB helicase from unwinding the C6 <ref name = "Bastia"> Bastia, D., Zzaman, S., Krings, G., Saxena, M., Peng, X. and Greenberg, M. (2008) Replication termination mechanism as revealed by Tus-mediated polar arrest of a sliding helicase. Proceedings of the National Academy of Science, USA, 105 (93): 12831-12836.</ref>. Despite this inability to unwind and from a locked complex with ''Tus'', polar fork termination is still permitted indicating that the formation of a locked complex is unnecessary for replication termination. | ||
==='''Current Models'''=== | ==='''Current Models'''=== | ||
Recent models for the termination of replication in ''E. coli'' propose that when DnaB approaches the Tus-''Ter'' complex from the permissive face there are no considerable protein-protein interactions between the DnaB and Tus resulting in the dislodgement of Tus from ''Ter'' and hence allowing for the progression of the replication fork. However, when DnaB approaches the non-permissive face, significant protein-protein interactions between the DnaB and Tus prevent the dislodgement of Tus, resulting in replication termination. If for any reason this mechanism may fail, DnaB will unwind ''Ter'' until it reaches C6 which would induce the formation of a locked complex and subsequent prevention of replication fork progression. | Recent models for the termination of replication in ''E. coli'' propose that when DnaB approaches the Tus-''Ter'' complex from the permissive face there are no considerable protein-protein interactions between the DnaB and Tus resulting in the dislodgement of Tus from ''Ter'' and hence allowing for the progression of the replication fork. However, when DnaB approaches the non-permissive face, significant protein-protein interactions between the DnaB and Tus prevent the dislodgement of Tus, resulting in replication termination. If for any reason this mechanism may fail, DnaB will unwind ''Ter'' until it reaches C6 which would induce the formation of a locked complex and subsequent prevention of replication fork progression <ref name = "Kaplan" />. | ||
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