Origin of replication
From Free net encyclopedia
The origin of replication (also called the replication origin) is a unique DNA sequence at which DNA replication is initiated. DNA replication may proceed from this point bidirectionally or unidirectionally.
The specific structure of the origin of replication varies somewhat from species to species, but all share some common characteristics. The origin of replication binds a member of the pre-replication complex—a protein complex that binds, unwinds, and begins to copy DNA.
The two types of replication origin are :
- Narrow or broad host range
- High- or low-copy number
Prokaryotes have a single circular molecule of DNA, and typically only a single origin of replication . Eukaryotes often have multiple origins of replication on each chromosome. Having many origins of replication helps to speed the duplication of their (usually) much larger store of genetic material. The segment of DNA that is copied starting from each unique replication origin is called a replicon.
Origins of replication are typically assigned names containing "ori". For example, the E. coli replication origin is known as oriC. In E. coli, the oriC consists of 13 mer repeats followed by 9 mer repeats. A protein, DnaA would bind to the 9 mer repeats, and the DNA would then coil around the protein complex (many DnaA) forming a protein core. This coiling stimulates the AT rich region in the 13 mer sequence to unwind, thus allowing enzymes and other factors to bind and replication would start.