DNA repair; translesion DNA synthesis

polymerase activity. These two functions together allow DNA polymerase III to efficiently and accurately synthesize new DNA molecules.

The first E. coli polymerase to be discovered, DNA polymerase I, also has 5': 3' polymerase and 3': 5' exonuclease activities (see Table 12.3), permitting the enzyme to synthesize DNA and to correct errors. Unlike DNA polymerase III, however, DNA polymerase I also possesses 5': 3' exonuclease activity, which is used to remove the primers laid down by primase and to replace them with DNA nucleotides by moving in a 5': 3' direction. The removal and replacement of primers appear to constitute the main function of DNA polymerase I. DNA polymerases IV and V function in DNA repair.

Despite their differences, all of E. coli's DNA polymerases

1. synthesize any sequence specified by the template strand;

2. synthesize in the 5': 3' direction by adding nucleotides to a 3'-OH group;

3. use dNTPs to synthesize new DNA;

4. require a primer to initiate synthesis;

5. catalyze the formation of a phosphodiester bond by joining the 5' phosphate group of the incoming nucleotide to the 3'-OH group of the preceding nucleotide on the growing strand, cleaving off two phosphates in the process;

6. produce newly synthesized strands that are complementary and antiparallel to the template strands; and

7. are associated with a number of other proteins.

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