TY - JOUR
T1 - Adaptive increase of O6-methlguanine-acceptor protein in HeLa cells following N-methyl-N′-nitro-N-nitrosoguanidine treatment
AU - Waldstein, Evelyn A.
AU - Cao, En Hua
AU - Setlow, Richard B.
PY - 1982/8/11
Y1 - 1982/8/11
N2 - 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).
AB - 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).
UR - http://www.scopus.com/inward/record.url?scp=0020480493&partnerID=8YFLogxK
U2 - 10.1093/nar/10.15.4595
DO - 10.1093/nar/10.15.4595
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C2 - 7133992
AN - SCOPUS:0020480493
SN - 0305-1048
VL - 10
SP - 4595
EP - 4604
JO - Nucleic Acids Research
JF - Nucleic Acids Research
IS - 15
ER -