Bacterial Replication Termination: Difference between revisions
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In most bacterial DNA replication, initiation occurs at an origin where, due to the circular nature of the chromosome, the replication forks move bidirectionally to end at approximately 180 degrees away, at a specific sequence termini region [1]. Bacterial replication termination systems have been well studied in ''Eschericia coli'' and ''Bascillus subtilis''. In both systems a ''trans''-acting replication termination protein binds to a specific ''cis''-acting DNA sequences; the replication termini (''ter''), and the DNA-protein complex arrests the progression of replication forks [2]. The terminator sites are orientated so that protein binding is asymmetric, allowing the complexes to block the replication machinery from only one direction while letting them proceed unimpeded from the other direction [1]. In this way they are said to act in a polar manner. The proteins involved in this termination are non-homologous and differ structurally in ''E.coli'' and ''B.subtilis'', although each contains similar contrahelicase activity and performs similar functions in arresting replication [1]. | In most bacterial DNA replication, initiation occurs at an origin where, due to the circular nature of the chromosome, the replication forks move bidirectionally to end at approximately 180 degrees away, at a specific sequence termini region [1]. Bacterial replication termination systems have been well studied in ''Eschericia coli'' and ''Bascillus subtilis''. In both systems a ''trans''-acting replication termination protein binds to a specific ''cis''-acting DNA sequences; the replication termini (''ter''), and the DNA-protein complex arrests the progression of replication forks [2]. The terminator sites are orientated so that protein binding is asymmetric, allowing the complexes to block the replication machinery from only one direction while letting them proceed unimpeded from the other direction [1]. In this way they are said to act in a polar manner. The proteins involved in this termination are non-homologous and differ structurally in ''E.coli'' and ''B.subtilis'', although each contains similar contrahelicase activity and performs similar functions in arresting replication [1]. | ||
[[Image:Bidirectionalrep2.jpg | thumb | right | 500px | Bacterial replication fork [3]]] | [[Image:Bidirectionalrep2.jpg | thumb | right | 500px | Bacterial replication fork [3]]] | ||
==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]]] | ||
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]. | ||
==Replication Terminator Protein (''Bacillus subtilis'')== | ==Replication Terminator Protein (''Bacillus subtilis'')== | ||
Replication Termination Protein (RTP), found in ''Bacillus subtilis'', is a member of the ‘winged helix’ protein family, and terminates bacterial DNA replication by arresting the replication forks through interactions with DNA in a sequence specific manner [7]. RTP blocks the replication fork through contrahelicase activity; the ability to specifically inhibit the helicase replication machinery and has an additional role in arresting transcription [1][2]. In ''B. subtilis'' the bipartite ''ter'' sequence is overlapping, and each inverted repeat contains core (IRIB) and an auxillary (IRIA) sites [1]. RTP binds to these sequences, resulting in the impediment the replication fork helicase. | <StructureSection load='1f4k' size='500' side='right' | CAPTION="The Replication Terminator Protein (RTP) complexed to it's ''ter'' site [[1f4k]]" | scene='User:Bianca_Varney/Bacterial_Replication_Termination/Opening_rtp/1'>Replication Termination Protein (RTP), found in ''Bacillus subtilis'', is a member of the ‘winged helix’ protein family, and terminates bacterial DNA replication by arresting the replication forks through interactions with DNA in a sequence specific manner [7]. RTP blocks the replication fork through contrahelicase activity; the ability to specifically inhibit the helicase replication machinery and has an additional role in arresting transcription [1][2]. In ''B. subtilis'' the bipartite ''ter'' sequence is overlapping, and each inverted repeat contains core (IRIB) and an auxillary (IRIA) sites [1]. RTP binds to these sequences, resulting in the impediment the replication fork helicase. | ||
====RTP Structure==== | ====RTP Structure==== | ||