Sandbox20
IntroductionIntroduction
Replication Termination in E. coli and B. subtilisReplication Termination in E. coli and B. subtilis
Replication forks proceed from the origin of the circular chromosome in opposite directions, creating a characteristic theta structure . Although the use of two active polymerase complexes is clearly faster than one, this mechanism generates difficulty when it comes to terminating replication. Among other factors, the presence of DNA-associated proteins causes the two replication complexes to proceed at different rates, and they therefore do not necessarily meet directly opposite the origin. However, the position of termination is not random, and is defined by the presence of termination sites which associate protein factors capable of halting the advance of the replication fork from only one direction. From their positions within the chromosome and their directionality, you can see that this occurs only once the complex has traversed more than half of the total DNA.
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The ProteinsThe Proteins
RTPRTP
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This is the area for text about RTP.
The condensed alpha/beta structure is .
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TusTus
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This is the area for text about Tus.
Structural OverviewStructural Overview
Original picture is .
DNA BindingDNA Binding
Tus binds by an interaction between beta sheets (shown in green) and the major groove of DNA. This is .
Anti-helicase ActivityAnti-helicase Activity
Tus binds to a conserved cytosine residue which is not base paired . The interactions between residues of the Tus protein and this unpaired cytosine nucleotide are shown in more detail .
Its ability to do this depends on the conserved glutamate residue E49. "The crystal structure of the Tus-Ter lock shows that Glu49 of Tus makes a water-mediated hydrogen bond with the 50- phosphate of the displaced A(7) nucleotide residue, and it would thus be expected to be partially defective in formation of the locked species." This is shown
E49K does not affect DNA binding but does affect anti-helicase activity in the ‘trapped’ complex E49 makes an indirect hydrogen bond to the phosphate of the ‘displaced’ nucleotide.