Intracellular localization of human DNA repair enzyme methylguanine-DNA methyltransferase by antibodies and its importance.

The human DNA repair enzyme, methylguanine-DNA methyltransferase (MGMT, M(r) 21,000), which protects cells against the mutagenic effect of alkylating carcinogens, was found to be localized in the cell nucleus (except the nucleolus) by immunofluorescence staining using polyclonal and monoclonal antibodies. The supporting experiments came from differential staining of the MGMT-deficient (mer-) and -proficient (mer+) cells, Western blotting analysis, and specific antibody depletion studies with the immobilized fusion protein, GSTMGMT-glutathione-Sepharose. Its localization in the nucleus agrees with its biological function and possibly explains the ineffective protection of mammalian cells (mer-) transfected with the Escherichia coli MGMT genes from bifunctional alkylating agents.