Figure 3. The α subunit of Mtb DNA Pol III has exonuclease activity.

(a) Exonuclease assays indicate that the α subunit is a 3′–5′ exonuclease which is activated by Mg²⁺, and inhibited by EDTA, Ca²⁺, Mn²⁺, Zn²⁺ and Co²⁺. (b) Assay of the exonuclease activity of the α subunit in the presence of Mg²⁺ combined with other divalent metal ions. The presence of Mg²⁺ does not affect the sensitivity of the exonuclease activity of the α subunit to Ca²⁺, Mn²⁺, Zn²⁺ or Co²⁺. (c) The DNA Pol III α subunit is a single-stranded DNA exonuclease as determined by assays using ssDNA, blunt-dsDNA or 5′ overhanging-dsDNA as substrates. Substrate types are shown above each panel. Results presented are representative of at least three replicate experiments.