To initiate the purification of DNA polymerase, the researchers added streptomycin sulfate to the E. coli extract.

The P-fraction also contained Pol I and heat-stable factors essential for the DNA synthesis reactions.

E. coli DNA Pol I consists of multiple domains with three distinct enzymatic activities.

One of the metal ions activates the primer 3' hydroxyl group, which then attacks the primary 5' phosphate of the dNTP.

The second metal ion will stabilize the leaving oxygen's negative charge, and subsequently chelates the two exiting phosphate groups.

However, the mutant strain also displayed characteristics which involved extreme sensitivity to certain factors that damaged DNA, like UV light.

It is a template-dependent enzyme—it only adds nucleotides that correctly base pair with an existing DNA strand acting as a template.

Nevertheless, Pol I can fix this error in DNA replication using its selective method of active discrimination.

Moreover, its cellular abundance of approximately 400 molecules per cell did not correlate with the fact that there are typically only two replication forks in E. coli.

Additionally, it is insufficiently processive to copy an entire genome, as it falls off after incorporating only 25–50 nucleotides.

[12] Cairns' lab assistant, Paula De Lucia, created thousands of cell free extracts from E. coli colonies and assayed them for DNA-polymerase activity.

The 3,478th clone contained the polA mutant, which was named by Cairns to credit "Paula" [De Lucia].

This undesirable enzymatic activity can be simply removed from the holoenzyme to leave a useful molecule called the Klenow fragment, widely used in molecular biology.