Termination of DNA replication

Content
Chemistry of the Gene 2.  Synthesis, Modification and Repair of DNA
DNA replication: general features 
Semi-conservative DNA replication in E. coli
Semi-conservative replication of chromosomes in eukaryotes
Semi-discontinuous DNA replication
Unidirectional and bidirectional DNA replication
RNA primers in DNA replication
Regulation of DNA replication by anti-sense RNA primer
Prokaryotic DNA polymerases
Eukaryotic DNA polymerases
Replicons for DNA replication
DNA replication in prokaryotes 
Experimental approaches for the study of DNA replication
Initiation of DNA replication
Elongation of DNA chain
Replication fork movement
Termination of DNA replication
DNA replication in eukaryotes 
DNA replication and cell cycle
Replication origins and initiation of DNA replication (cis and trans-acting elements)
Comparison of initiation of DNA replication with transcription initiation
Different steps involved in eukaryotic DNA replication
Synthesis of telomeric DNA by telomerase
Models of DNA replication
Replication fork model
Rolling circle model of DNA replication
Mitochondrial DNA replication and D-loops
RNA directed DNA synthesis (reverse transcription)
DNA modification and DNA restriction
DNA repair
Excision repair systems in E. coli
An SOS repair system in E. coli
DNA repair and genetic diseases in humans


Termination of DNA replication
The E. coli chromosome carries a large termination zone, diametrically opposite from oriC, which blocks the progress of replication forks (of bidirectional replication), meeting at this region. E. coli chromosome and several plasmids carry specific sequences, called ter sites, where TBP, (ter binding protein) or 'Tus protein' binds. In the termination zone of E. coli, there are three ter sites (ter A, ter D and ter E)for counter-clockwise fork and three ter sites (ter B, ter C and ter F)for clockwise fork. These six sites are arranged in overlapping manner, leaving no 'replication-free' gap on the chromosome (Fig. 26.22). TBP-ter complexes formed at 'ter' sites stalls the replication fork, by inhibiting the DNA helicase or DnaB.When this termination zone is deleted, replication stops simply by the meeting of opposite replication forks, suggesting that the termination zone is not essential.
 
A partial map of E, coli chromosome, showing the position of six termination sites (terA-terF)and the tus gene relative to the location of oriC.
Fig. 26.22. A partial map of E, coli chromosome, showing the position of six termination sites (terA-terF)and the tus gene relative to the location of oriC.