The key features of DNA polymerase III are its catalytic potency, its fidelity, and its processivity. It is able to catalyze the addition of ~103 bases per second, compared to only about 10 per second for DNA polymerase I,with an error frequency of about 1:104– 105. One of the unique features of DNA polymerase III is its ability to continuously synthesize very long (thousands of bases) stretches of DNA, unlike DNA polymerase I. This is a consequence of its processivity; the β2 sliding clamps ensure that it remains bound to the template strand DNA.
In contrast, DNA polymerase I, without a sliding clamp, is much more likely to dissociate from the template strand after synthesis of short (tens of bases) stretches of DNA.