Building a bacterial orisome: emergence of new regulatory features for replication origin unwinding

Abstract

SummaryTriggering new rounds of chromosomal DNA replication during the bacterial cell cycle is exquisitely regulated, ensuring both proper timing and one round per cycle stringency. A critical first step is stable unwinding of oriC , the chromosomal replication origin, by multiprotein orisome complexes comprising the AAA + initiator DnaA and modulator proteins that bend DNA. Recently identified oriC -DnaA interactions in Escherichia coli raise important questions regarding the molecular mechanisms that regulate origin unwinding in bacteria. We describe staged binding of E. coli origin recognition proteins and suggest an unwinding switch based on interactions between DnaA-ATP and specialized oriC sites that must be filled during orisome assembly. By focusing multiple regulatory pathways on only a few key oriC DNA-protein interactions, this model includes an efficient way to control unwinding followed by orisome inactivation during the cell cycle. Future studies will determine whether this regulatory scheme is correct and whether it is generally applicable to other bacterial types.

Mycobacterium tuberculosis Origin of Replication and the Promoter for Immunodominant Secreted Antigen 85B Are the Targets of MtrA, the Essential Response Regulator

“…It is pertinent to note that in E. coli cells, DnaA persistently binds to the high affinity DnaA-boxes in oriC, but the key low affinity DnaA-boxes are unoccupied until they are required during the initiation of chromosome replication. This high to low affinity DnaA-box hierarchy is an important part of the E. coli oriC regulatory system (44). The Caulobacter crescentus response regulator CtrA binds five sites spread across its replication origin (45).…”

A Role for Nonessential Domain II of Initiator Protein, DnaA, in Replication Control

“…Although DnaA levels appear not to fluctuate during the cell cycle, the onset of replication is regulated by the ATP-bound state of the protein or its interaction with binding sites in oriC (reviewed in Messer 2002; Leonard and Grimwade 2005;Kaguni 2006;Katayama 2008). The SeqA protein sequesters the origin immediately after initiation due to its cooperative binding to hemi-methylated GATC sites, found in abundance near the origin (Campbell and Kleckner 1990;Lu et al 1994;von Freiesleben et al 2000).…”

“…a number of factors that regulate the activity of the the AAA1 DnaA protein (reviewed in Messer 2002; Leonard and Grimwade 2005;Kaguni 2006;Katayama 2008), the functional and structural equivalent of eukaryotic Cdc6/Orc proteins. DnaA binds to several high-affinity binding sites, known as DnaA boxes, near the origin of replication, oriC, in Escherichia coli.…”

Understanding Protein Function - The Disparity Between Bioinformatics and Molecular Methods

“…The influence of IHF, FIS, IciA, Rob and SeqA proteins on the initiation process is described in more detail in a review (Leonard and Grimwade, 2005). At the initiation stage of DNA replication, the first step requires the binding of DnaA molecules, each complexed to ATP, to the five DnaA boxes, I-and τ-sites of oriC.…”