The KatG enzyme, like most hydroperoxidase I (HPI)-type catalases, consists of two related domains, each with strong similarity to the yeast cytochrome peroxidase. The catalase-peroxidase activity is associated with the amino-terminal domain but currently no definite function has been assigned to the carboxy-terminal domain, although it may play a role in substrate binding. This paper reports another possible function of the KatG protein involving protection of the host cell against DNA-damaging agents. The gene, the 5′ domain and the 3′ domain were cloned separately, in-frame with the maltose-binding protein, into the vector pMAL-c2. These constructs were introduced into four DNA-repair mutants of , DK1 (), AB1884 (), AB1885 () and AB1886 (), which were then tested for their ability to survive treatment with UV light (254 nm), hydrogen peroxide (1·6 mg ml) and mitomycin C (6 μg ml). All three constructs conferred resistance to UV upon the cells, whereas resistance to mitomycin C was found in all repair mutants tested. Protection against hydrogen peroxide damage was less pronounced and predominantly found in the host. These results indicated that the gene can enhance DNA repair in , and that the 5′ and 3′ domains can function separately. UV sensitivity tests on and strains mutant in revealed that the gene product does not play an additive role in the survival of mycobacterial cells after exposure to short-wavelength UV irradiation, in repair-competent cells.


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