|MoBio||Overview of DNA Replication||Chapter 7|
DNA replication is triggered by the expression of all required proteins, such as DNA polymerase, DNA primase, and cyclin. In yeast, the transcription factor regulating the expression of these proteins is called MCB binding factor. In mammals, the corresponding transcription factor is E2F.
Gene transcription starts from the promoter, proceeding along one direction, whereas the DNA replication starts from the replication origin, proceeding along both directions. There is only one replication origin in the genomic DNA of E. coli (Figure 3-H-3), but the eukaryotic DNA contains many replication origins in each chromosome.
In E. coli, movement of the growing fork is about 1000 bp per second. It takes about 42 minutes to duplicate the entire genomic DNA. In eukaryotic DNA, the fork movement is only about 100 bp per second. This is probably due to the association of DNA with histones, which may hinder the fork movement. In humans, replication of the entire genome requires about 8 hours. In fruit flies, it takes only 3 - 4 minutes.
Based on computer analysis, the consensus sequence of human replication origin is WAWTTDDWWWDHWGWHMAWTT, where W = A or T; D = A, G or T ; H = A, C or T, and M = A or C.
Note that "A" and "T" dominate the replication origin. This is because the A-T pair is linked by two hydrogen bonds while C-T pair by three hydrogen bonds (Figure 3-B-1). Therefore, the region dominated by "A" and "T" should be easier to unwind.