6/ 💡 Proposed model
Before crtS replication: ori2 is OFF, blocked by inhibitory RctB-DNA loops.
After crtS replication: inhibition is destabilized, ori2 becomes accessible, and Chr2 replication begins.
A beautiful molecular ON/OFF switch! 🕹️

5/ 🗝️ crtS: The key
After crtS is replicated on Chr1, RctB shifts to activation sites (iterons), unlocking Chr2 replication. Each crtS replication event triggers replication of a single ori2. This ensures a precise one-to-one synchronization between Chr1 and Chr2.

4/ 🔒 RctB: The gatekeeper (part II)
Cryo-EM and X-ray crystallography revealed that RctB oligomerizes through two key interfaces in its domain IV, enabling the formation of higher-order complexes that stabilize the inhibitory DNA loops at ori2.

4/ 🔒 RctB: The gatekeeper (part I)
ChIP-seq revealed that RctB binds to inhibitory sites (29/39m) on Chr2’s origin, blocking Chr2 replication for most of the cell cycle. Using TEM, we observed how RctB forms large nucleoprotein complexes at ori2. These complexes bridge 29/39m sites, creating loops.

3/ 🧩 The methods
To investigate this mechanism, we mapped the binding of RctB (the initiator for Chr2 replication) across the genome at different points in the cell cycle using ChIP-seq. This was combined with live-cell microscopy, transmission electron microscopy and structural studies.

1/ 🔬 Our work, "Dynamic transitions of initiator binding coordinate the replication of the two chromosomes in Vibrio cholerae", is now published in Nature Communications.
Here's a thread on how we think Chr1 and Chr2 replication is coordinated in Vibrio. 🧵

Link : www.nature.com/articles/s41...