Final answer:
DnaA-ATP is the protein that opens dsDNA at oriC by melting the strands apart, enabling helicase to further unwind the DNA for replication. Single-stranded binding proteins and topoisomerases play crucial roles in maintaining strand separation and resolving supercoiling, respectively.
Step-by-step explanation:
The protein that opens double-stranded DNA (dsDNA) at the origin of replication (oriC) in E. coli by melting the two strands apart is DnaA-ATP. This initiation protein binds to specific sequences within the oriC and utilizes the energy from ATP to destabilize and open the double helix, creating a single-stranded region. Ensuing this, helicase, specifically DnaB helicase in E. coli, is then able to unwind the DNA further, utilizing ATP hydrolysis to progress the replication forks bidirectionally.
Once the DNA strands are separated, single-stranded binding proteins (SSBs) coat the strands to prevent them from reannealing. Topoisomerases, such as DNA gyrase, mitigate the supercoiling that occurs ahead of the replication fork by cutting and rejoining the DNA strands, allowing the helix to spin and relax.