RTP and Tus: Difference between revisions
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<Structure load='2I06' size='400' frame='true' align='right' caption='Tus | <Structure load='2I06' size='400' frame='true' align='right' caption='Locked Tus-''Ter'' Complex (Mulcair ''et al'' 2006)' scene='RTP_and_Tus/Co-ordination_of_his144/7' /> | ||
== Tus: an asymmetric monomer, and unlikely candidate. == | == Tus: an asymmetric monomer, and unlikely candidate. == | ||
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Mulcair ''et al'' (2006) discovered that the key to Tus forming a locked complex with ''Ter'' was twofold: firstly, the locked complex was formed only on the approach of DnaB helicase (the leading edge of the replication fork), and secondly, this locked complex was due to the base-flipping of C6 of ''Ter'' DNA into a cytosine-specific binding pocket on Tus. The approach of DnaB is essential to lock formation as strand separation is required before the C6 base can twist out of the helix; this base is on the displaced strand, which explains why strand displacement by DnaB is halted. This C6 binds somewhere near the α4 helix, in or near the DNA-binding channel. Mulcair ''et al'' also showed that while this conformational change occurs at the non-permissive end of the complex when "locked", the interdomain and permissive face remain in a similar conformation to the non-locked complex. | Mulcair ''et al'' (2006) discovered that the key to Tus forming a locked complex with ''Ter'' was twofold: firstly, the locked complex was formed only on the approach of DnaB helicase (the leading edge of the replication fork), and secondly, this locked complex was due to the base-flipping of C6 of ''Ter'' DNA into a cytosine-specific binding pocket on Tus. The approach of DnaB is essential to lock formation as strand separation is required before the C6 base can twist out of the helix; this base is on the displaced strand, which explains why strand displacement by DnaB is halted. This C6 binds somewhere near the α4 helix, in or near the DNA-binding channel. Mulcair ''et al'' also showed that while this conformational change occurs at the non-permissive end of the complex when "locked", the interdomain and permissive face remain in a similar conformation to the non-locked complex. | ||
<scene name='RTP_and_Tus/Co-ordination_of_his144/ | <scene name='RTP_and_Tus/Co-ordination_of_his144/7'>His144</scene> is a particularly important residue - it exists as its conjugate acid in the locked complex, forming hydrogen bonds with C6. Other residues - for example Phe140 and Gly149 - are also strictly conserved amongst different species' Tus protiens; many of the conserved residues among different ''Ter'' sites make base-specific contacts with Tus. | ||
The locked Tus-''Ter'' complex is the most stable known monomeric DNA binding protein with a double-stranded sequence-specific recognition sequence - a half life of 550min has been reported (Mulcair, 2006). The formation of a large hydrogen-bond network is critical to sequence recognition and the stability of the twisted β-strands lying across the major groove.<ref>Mulcair et al (2006) A Molecular Mousetrap Determines Polarity of Termination of DNA Replication in E. coli, Cell 125: 1309 - 1319 | The locked Tus-''Ter'' complex is the most stable known monomeric DNA binding protein with a double-stranded sequence-specific recognition sequence - a half life of 550min has been reported (Mulcair, 2006). The formation of a large hydrogen-bond network is critical to sequence recognition and the stability of the twisted β-strands lying across the major groove.<ref>Mulcair et al (2006) A Molecular Mousetrap Determines Polarity of Termination of DNA Replication in E. coli, Cell 125: 1309 - 1319 | ||
</ref> | </ref> | ||
