Adaptive increase of O6-methlguanine-acceptor protein in HeLa cells following N-methyl-N′-nitro-N-nitrosoguanidine treatment

Evelyn A. Waldstein, En Hua Cao, Richard B. Setlow

Research output: Contribution to journalArticlepeer-review

Abstract

We have assayed in extracts of HeLa cells the amount of acceptor protein that removes O6-methylguanine adducts from alkylated DNA. Cells were treated with single or multiple nontoxic doses of N-methyl-N′-nitro-N-nitrosoguanidine (MNNG) and the extracts were analyzed up to 32 h after the last exposure. The acceptor activity assayed immediately (1 h) after single exposures decreases linearly with dose indicating that the acceptor protein is used up by endogenous O6-methylguanine adducts in a stoichiometric reaction. Multiple exposures, assayed 8-24 h after the last exposure, increase the amount of acceptor protein in a dose dependent fashion followed by a decrease above a cumulative dose of 100 ng/ml. Under conditions of maximum induction, there are about 300,000 acceptor protein sites per cell, approximately 3 fold above the constitutive level. Both in adapted and unadapted cells the methyl group from O6-methylguanine adducts in the alkylated DNA is transferred to cysteine residues of the acceptor protein(s).

Original languageEnglish
Pages (from-to)4595-4604
Number of pages10
JournalNucleic Acids Research
Volume10
Issue number15
DOIs
StatePublished - 11 Aug 1982
Externally publishedYes

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