The origin of replication (oriC) is the specific sequence on the prokaryotic chromosome where DNA replication initiates. It's not a protein that binds, but rather a specific DNA sequence that is recognized by proteins involved in the initiation of replication.

Here's a breakdown:

1. oriC: This sequence is rich in AT base pairs, making it easier to unwind than GC-rich regions.

2. Initiator proteins: In *E. coli*, these are DnaA proteins. They bind to specific 9-mer sequences within oriC, causing the DNA to bend and unwind.

3. Unwinding: This unwinding creates a replication bubble, where the two strands of DNA are separated and accessible for replication.

4. Helicases and other proteins: Other proteins like helicase (DnaB in *E. coli*) and single-stranded binding proteins (SSBs) further unwind the DNA and stabilize the single-stranded regions.

5. Primase: This enzyme lays down short RNA primers, providing a starting point for DNA polymerase to begin synthesizing new DNA strands.

So, while it's not a protein binding to the chromosome *start*, it's a specific DNA sequence (oriC) that attracts proteins responsible for starting the replication process.