Replicative DNA polymerases (EC 2.7.7.7) are the key enzymes catalyzing the
accurate replication of DNA. They require either a small RNA molecule or a
protein as a primer for the de novo synthesis of a DNA chain. On the basis of
sequence similarities a number of DNA polymerases have been grouped together
[1,2,3] under the designation of DNA polymerase family A. The polymerases that
belong to this family are listed below.
- Escherichia coli and various other bacterial polymerase I (gene polA).
- Thermus aquaticus Taq polymerase.
- Bacteriophage sp01 polymerase.
- Bacteriophage sp02 polymerase.
- Bacteriophage T5 polymerase.
- Bacteriophage T7 polymerase.
- Mycobacteriophage L5 polymerase.
- Yeast mitochondrial polymerase γ (gene MIP1).
Five regions of similarity are found in all the above polymerases. One of
these conserved regions, known as 'motif B' [1], is located in a domain which,
in Escherichia coli polA, has been shown to bind deoxynucleotide triphosphate
substrates; it contains a conserved tyrosine which has been shown, by photo-affinity labelling, to be in the active site; a conserved lysine, also part of
this motif, can be chemically labelled, using pyridoxal phosphate. We use this
conserved region as a signature for this family of DNA polymerases.
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