Existing strands of DNA function as templates during replication, the process by which cells make an exact copy of their genetic material. DNA strands have a 5’ and 3’ end, and the two strands that comprise a DNA double helix run antiparallel to each other. Replication begins at particular sequences throughout the genome known as origins of replication, and these regions of the genome are bound by an origin recognition complex that includes the proteins ORC 1-6, during of cell division1. A pre-replicative complex assembles at each origin at the end of mitosis, and this complex consists of multiple proteins that serve as a scaffold for proteins essential for DNA replication to begin again during the next cell cycle2. Enzymes, including helicase, which unwinds the DNA, and DNA polymerase, which adds new bases onto the growing strand, are then recruited, and become a part of a multiprotein complex known as the replication fork. The replication fork migrates along the double-stranded DNA, and new strands are synthesized in the 5’ to 3’ direction. Due to the antiparallel orientation of the double helix, the strand oriented in the 3’ to 5’ direction undergoes continuous replication and is referred to as the leading strand, while the strand oriented in the 5’ to 3’ direction undergoes discontinuous replication and is known as the lagging strand. While replication of the leading strand results in one new strand of DNA, replication of the lagging strand results in short DNA fragments known as Okazaki fragments, which are subsequently joined together by DNA ligase I. Finally, the four lengths of single-stranded DNA that exist at the end of replication are ligated to form two new double helices. Each double-stranded helix consists of one strand of template DNA and the strand that was synthesized from it; hence, DNA replication is referred to as a semi-conservative process3.
Three crucial enzymes for the DNA replication process are helicases, polymerases, and ligases. Helicases can be grouped into two superfamilies that are involved in numerous cellular processes that require access to single-stranded DNA, including replication4. The structure of helicases appears to have evolved in such a way that helicases found in organisms today exhibit a greater specificity for nucleotides than in the past. DNA polymerases are a class of enzymes involved in adding nucleotides to newly forming strands of DNA in the 5’ to 3’ direction. The first DNA polymerase was identified in E. coli in the 1950s5, 6, and it has since been realized that the protein sequence and molecular weight of DNA polymerases are highly conserved across species, from protozoa to humans7. Several classes of DNA polymerases exist in prokaryotes and eukaryotes, including 5 in E. coli, 12 in some plant species, and 15 or more in humans8. DNA ligases form the phosphodiester bonds between nucleotides on single-stranded or double-stranded DNA, during DNA replication and other cellular processes related to repairing breaks in the DNA. The domain of DNA ligases that recognizes breaks between nucleotides and catalyzes their joining appear to be conserved across species9.
Below is the entire list of targets involved in DNA replication research. Can't find what you are looking for? Bethyl offers a custom antibody service.