Concerted actions of DnaA complexes with DNA-unwinding sequences within and flanking replication origin oriC promote DnaB helicase loading

Thermotoga maritima oriC involves a DNA unwinding element with distinct modules and a DnaA-oligomerizing region with a novel directional binding mode

“…The DnaA proteins may therefore have evolved to bind to the transiently distorted TA, thereby stabilizing the unwound DNA. This is consistent with results showing that the TTATT motif with a central TA dinucleotide, instead of TAG, is present in E. coli DUE ( 7 , 17 ). Intriguingly, TAG repeats have been observed in human telomeric DNA.…”

“…Besides, the unwound region of tmaDUE may further expand over the TTATT and DnaA-trio motifs for stable unwinding and subsequent helicase loading. Expansion of the unwinding regions has been well characterized in open complexes of E. coli ( 7 ). This proposed mechanism is also fully consistent with the mechanism underlying ssDUE recruitment.…”

“…1 A ). The ATP-bound DnaA oligomers of the DOR are important for DUE unwinding and loading of DnaB replicative helicase onto the unwound region ( 5 , 7 , 8 , 9 , 10 , 11 ).

Figure 1 Models for unwinding of the replication origin in eubacteria .

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“…1 B ). DnaA complexes in the right DOR are important for enhancement of the unwound state and efficient DnaB loading ( 7 , 9 ).…”

“…In E. coli , the ATP-DnaA–IHF–Left-DOR complexes are responsible for the unwinding of DUE. The upper strand of the resulting ssDUE is subsequently recruited to the ATP–DnaA pentamers through IHF binding-induced DOR bending, which directs interactions between the H/B-motifs of DnaA and ssDUE, resulting in open complex formation ( 7 , 9 , 17 , 26 ) ( Fig. 1 , A and B ).…”