Termination of Replication in Bacteria

Abstract

In the case of a circular bacterial chromosome, termination of DNA replication occurs when the two replication forks, progressing in opposite directions, meet and fuse in a specific region of the chromosome, which is generally diametrically opposed to the site of initiation of DNA replication. Most research has focused on the systems utilized by the rod‐shaped Gram‐negative Escherichia coli and Gram‐positive Bacillus subtilis.

Keywords: DNA replication; replication termination; replication fork arrest; DNA terminators; replication terminator protein; termination utilization substance; catenanes

Figure 1.

Arrangement of DNA replication terminators in the circular chromosomes of (a) Escherichia coli and (b) Bacillus subtilis. The two replication forks generated at the origin (oriC) move in opposite directions along the DNA and eventually approach one other and fuse within the terminus region diametrically opposed to oriC. The terminus region constitutes a replication fork trap in which the DNA terminators (denoted Ter) are arranged as two opposed groups, with the purple terminators oriented to block movement of the clockwise replication fork and the green terminators oriented to block the anticlockwise fork. The STer region contains additional terminator sites used by B. subtilis only during the stringent response. The approximate chromosomal locations of the genes for the terminator proteins, Tus (terminus utilization substance) in E. coli and RTP (replication terminator protein) in B. subtilis, are marked with arrows. (c) Consensus sequence for the B. subtilis terminators, with the overlapping A and B sites indicated.

Figure 2.

Tus–Ter fork arrest complex (Kamada et al., ). (a) A view perpendicular to the helical axis of the DNA (red). Tus (terminus utilization substance) is composed of a large N‐terminal domain (blue) and a smaller C‐terminal domain (green) with an interdomain region (gold) that is composed of two very long β strands flanked by three smaller strands. In this view, the ‘passage end’ and the ‘blockage end’ are indicated. (b) A view down the helical axis of the DNA from the blockage end of the fork‐arrest complex; this view can be obtained by a 90° leftwards rotation of the view in (a). The L1 loop (indicated) has been implicated in taking part in a specific interaction with the replicative helicase during fork arrest (Henderson et al., ; Mulugu et al., ), whereas the two bulky α‐helical domains, suggested sterically to block replisome movement in the alternative model, dominate this ‘helicase eye’ view.

Figure 3.

Crystal structure of a replication terminator protein (RTP) dimer bound to DNA (a, b) and a model of the complete RTP–Ter complex (c) (Wilce et al., ). (a) A view perpendicular to the helical axis of the DNA. The RTP dimer (green) has its secondary structural elements labelled on one of the RTP monomers. Each monomer has structural homology to other ‘winged‐helix’ DNA‐binding protein family members, with the α3 helix from each monomer making the most significant base‐specific contacts. The long α4 helices from each monomer form the coiled‐coil dimerization domain. (b) A view down the helical axis of the DNA; this view can be obtained by a 90° y‐axis rotation of the view in (a). (c) A model of the complete RTP–Ter complex based on the crystal structure of the RTP dimer–DNA complex and knowledge of the relative positioning of the two adjacent RTP‐binding sites within the TerDNA. Each dimer is shown as a backbone structure with a surface rendering. The model could explain how the two RTP dimers interact with one another when bound together at the terminator; contact could be mediated by a region comprising portions of the α3 helix and the β2 strand of adjacent RTP molecules – these structural elements are indicated in (b).

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References

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Further Reading

Duggin IG and Wake RG (2002) Termination of chromosome replication. Sonenshein AL (ed.) Bacillus subtilis and its Closest Relatives: From Genes To Cells, pp. 87–95. Washington, DC: ASM Press

Hill TM (1996) Features of the chromosomal terminus region. Neidhardt FC (ed.) Escherichia coli and Salmonella: Cellular and Molecular Biology, 2nd ed., pp. 1602–1614. Washington, DC: ASM Press

Sherratt DJ, Lau IF and Barre FX (2001) Chromosome segregation. Current Opinion in Microbiology 4: 653–659.

Vengrova S, Codlin S and Dalgaard JZ (2002) RTS1 – a eukaryotic terminator of replication. International Journal of Biochemistry and Cell Biology 34: 1031–1034.

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Duggin, Iain G, and Wilce, Jackie A(May 2005) Termination of Replication in Bacteria. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1038/npg.els.0003901]