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#bacterial replication

3 public questions tagged with this topic.

Replication in Prokaryotes

Replication in E. coli proceeds by

Chromosome replication in E. coli visualized historically by autoradiography resembles Greek letter theta, where central replication bubble expands between two diverging forks within circular duplex. As synthesis proceeds, unreplicated parental segment plus two replicated arms resemble theta shape. This contrasting model contrasts with sigma rolling circle mode used by many plasmids and phage lambda late replication where one end spills out as concatamer, and linear mode of eukaryotes with multiple origins. Theta mode preserves circular integrity and permits efficient bidirectional progression around circle.

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 5: Theta mode replication of circular bacterial chromosome

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Replication in Prokaryotes

Dam methylase methylates which sequence?

DNA adenine methyltransferase Dam transfers methyl groups to N6 position of adenine within palindromic sequence GATC widespread in E. coli genome occurring roughly every 256 base pairs randomly. After semiconservative replication, GATC becomes hemimethylated until Dam restores full methylation using S-adenosylmethionine. Transient state distinguishes nascent strand for mismatch repair strand discrimination and participates in origin sequestration via SeqA binding. Methylation does not affect base pairing but influences protein-DNA interactions altering binding affinities. Mutations in dam elevate mutations and asynchronous initiation.

Ref: Lodish et al., Molecular Cell Biology, 9th ed., Chapter 11: Dam methylase specificity for GATC and hemimethylation signal

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Replication Basics

Replication in E. coli is mainly

Escherichia coli chromosome replication initiates at single defined origin oriC and proceeds concurrently in both directions around circular map toward terminus region opposite origin. Terminus contains polar Ter sequences bound by Tus protein that arrest helicase, allowing forks to meet. Bidirectional progression doubles replication speed compared to unidirectional mode, ensures complete duplication within 40 minutes at 37°C. Theta intermediates seen by Cairns autoradiography demonstrate bidirectional bubble expansion. Although rolling circle replication occurs in conjugative plasmids, main chromosomal mode is definitively bidirectional, conserved across many bacteria and eukaryotic replicons.

Ref: Cairns J, J Mol Biol 1963: Replication in E. coli is Mainly Bidirectional, Theta Replication

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