Characteristics
of
DNA
Polymerases
1. In Prokaryotes there are three DNA Polymerases, I,II, and III. Eukaryote cell have three polymerases alpha ,β,γ
2. DNA Polymerases I has three activities: 5’-->3’ polymerization activity, 3’-->5’ exonuclease activity and 5’-->3’ exonuclease activity DNA polymerases II and III are reported to lack 5’-->3’ nuclease activity
3. Polymerization is the synthesis of a complementary DNA strand from deoxyribonucleoside triphosphate monomers. The strand grows in the 5'-->3' direction. The main polymerizing enzyme is polymerase III.
4. 3'-->5' exonuclease activity of polymerases I, II and In results in degradation of one of the DNA strands in the 3'-->5' direction. It has an 'editing' function by removing incorrectly incorporated nucleotides.
5. 5'-->3' exonuclease activity results in excision of pyrimidine dimers (e.g. T=T) which are formed when DNA is exposed to ultraviolet light.
6. The templates for polymerase I are optimally single stranded regions of DNA, near double stranded regions. Polymerases II and III on the other hand prefer a template of double stranded DNA with short gaps.
