E. coli polymerases I, II, and III have 3' to 5' activity, which provides them with a proofreading function, i.e. they can remove a mispaired base.

The statement highlights an important feature of E. coli DNA polymerases I, II, and III, which possess 3' to 5' exonuclease activity. This activity is critical for the fidelity of DNA replication.

1. Proofreading Function: During DNA synthesis, these polymerases synthesize DNA in the 5' to 3' direction. If an incorrect nucleotide is incorporated, the polymerase can recognize the mismatch. The 3' to 5' exonuclease activity allows the polymerase to remove the mispaired base by moving backward and cleaving the bond.

2. Correct Base Pairing: After excising the erroneous nucleotide, the polymerase can then correctly insert the appropriate nucleotide, ensuring high fidelity in DNA replication.

3. Overall Importance: This proofreading mechanism significantly reduces the rate of mutations and enhances the accuracy of DNA replication. Without this activity, the replication process would be error-prone, leading to deleterious mutations and genomic instability.

In summary, E. coli polymerases I, II, and III ensure the integrity of genetic information through their proofreading ability, which is crucial for maintaining the fidelity of DNA replication.