DNA gene synthesis

DNA replication in prokaryotes

Initiation

The initiation is the first process of the replication. In other words, it is where the splitting actually begins. This is called “the origin of replication”. Let’s take a little closer look: The initiation of DNA replication is mediated by DnaA, a protein that binds to a region of the origin known as the DnaA box. In E. coli, there are 5 DnaA boxes, each of which contains a highly conserved 9 bp consensus sequence 5' - TTATCCACA - 3'. If you try binding of DnaA to this region it will cause it to become negatively supercoiled. The next step, of course is the region of OriC upstream of the DnaA boxes (known as DnaB boxes) which becomes melted.

Elongation

Once priming is complete, the next step is the DNA polymerase III holoenzyme is loaded into the DNA and replication begins. This might look complicated, but actually it’s very simple: The catalytic mechanism of DNA polymerase III involves the use of two metal ions in the active site, and a region in the active site that can discriminate between deoxyribonucleotides and ribonucleotides.


Termination

Keep in mind, that the termination of DNA replication in E. coli is completed through the use of termination sequences and the Tus protein. How do they work? It’s really simple: these sequences allow the two replication forks to pass through in only one direction, but not the other.

Regulation

Regulation of DNA replication is achieved through several mechanisms. Let’s take a closer look what these several mechanisms involve: The mechanisms involve the ratio of ATP to ADP, of DnaA to the number of DnaA boxes and the hemimethylation and sequestering of OriC. And there you have it, simple as ever.