Bacterial Replication Termination: Difference between revisions
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[[Image:Bidirectionalrep2.jpg | thumb | right | 500px | Bacterial replication fork [3]]] | [[Image:Bidirectionalrep2.jpg | thumb | right | 500px | Bacterial replication fork [3]]] | ||
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==Termination (''ter'') Sites== | ==Termination (''ter'') Sites== | ||
[[Image:Ecoli ter consensus.png | thumb | left | 350px | ''E. coli ter'' consensus [4]]] | [[Image:Ecoli ter consensus.png | thumb | left | 350px | ''E. coli ter'' consensus [4]]] | ||
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Replication is terminated in bacterial systems such as ''E.coli'' and ''B.subtilis'' by a "replication fork trap", studded with termination sites which causes the bidirectional forks to pause, encounter and fuse within a region called the terminus region [5]. In ''E.coli'' the termination regions are spread across nearly half the chromosome compared to ''B.subtilis'' where they cover only ~10%. In ''E.coli'' the 5 ''ter'' sites, J, G, F, B and C are arranged opposed to ''ter'' sites H, I, E, D and A, and can arrest the fork progressing in the clockwise direction and can block the anticlockwise direction, respectively [5]. The replication fork progressing in a clockwise direction will encounter the ''terC'' site first and pause. If the fork progressing from the anticlockwise direction meets the clockwise fork while paused, replication is terminated, however if it does not meet its anti-fork it will proceed until it reaches the next termination site, ''terB'', where it will pause again, etc [5]. Therefore multiple ''ter'' sites are important as infrequently utilized backups, to ensure that the fork does not leave the terminus region, and that termination is completed. Multiple regions to entrap the replication fork means that if an inactivating mutation arises within a ''ter'' site, then arrest can still occur at another ''ter'' sequence [6]. | Replication is terminated in bacterial systems such as ''E.coli'' and ''B.subtilis'' by a "replication fork trap", studded with termination sites which causes the bidirectional forks to pause, encounter and fuse within a region called the terminus region [5]. In ''E.coli'' the termination regions are spread across nearly half the chromosome compared to ''B.subtilis'' where they cover only ~10%. In ''E.coli'' the 5 ''ter'' sites, J, G, F, B and C are arranged opposed to ''ter'' sites H, I, E, D and A, and can arrest the fork progressing in the clockwise direction and can block the anticlockwise direction, respectively [5]. The replication fork progressing in a clockwise direction will encounter the ''terC'' site first and pause. If the fork progressing from the anticlockwise direction meets the clockwise fork while paused, replication is terminated, however if it does not meet its anti-fork it will proceed until it reaches the next termination site, ''terB'', where it will pause again, etc [5]. Therefore multiple ''ter'' sites are important as infrequently utilized backups, to ensure that the fork does not leave the terminus region, and that termination is completed. Multiple regions to entrap the replication fork means that if an inactivating mutation arises within a ''ter'' site, then arrest can still occur at another ''ter'' sequence [6]. | ||