Abstract
Chromosome replication in Escherichia coli is initiated by DnaA. DnaA binds ATP which is essential for formation of a DnaA-oriC nucleoprotein complex that promotes strand opening, helicase loading and replisome assembly. Following initiation, DnaAATP is converted to DnaAADP primarily by the Regulatory Inactivation of DnaA process (RIDA). In RIDA deficient cells, DnaAATP accumulates leading to uncontrolled initiation of replication and cell death by accumulation of DNA strand breaks. Mutations that suppress RIDA deficiency either dampen overinitiation or permit growth despite overinitiation. We characterize mutations of the last group that have in common that distinct metabolic routes are rewired resulting in the redirection of electron flow towards the cytochrome bd-1. We propose a model where cytochrome bd-1 lowers the formation of reactive oxygen species and hence oxidative damage to the DNA in general. This increases the processivity of replication forks generated by overinitiation to a level that sustains viability.
Highlights
Initiation of chromosome replication from the unique replication origin of E. coli oriC, is tightly controlled and happens once and only once per cell cycle [1, 2]
In most bacteria chromosome replication is initiated by the DnaA protein
We provide evidence that cell death in overinitiating cells can be prevented by rewiring the metabolism to favor the micro-aerobic respiratory chain with the cytochrome bd-1 as terminal oxidase
Summary
Initiation of chromosome replication from the unique replication origin of E. coli oriC, is tightly controlled and happens once and only once per cell cycle [1, 2]. DnaA associated with either ATP or ADP binds a set of strong recognition sites in oriC throughout the cell cycle [4] to form the origin recognition complex (ORC;[5]). Upon initiation the DnaA protein associated with ATP forms the orisome by binding to numerous additional sites in oriC. This displaces Fis (Factor for Inversion Stimulation), a protein that binds oriC for most of the cell cycle. With Fis gone, the IHF (Integration Host Factor) protein can bind oriC, which leads to duplex opening [6, 7], helicase loading and assembly of two replisomes [8]
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