Nucleic Acids Research, Vol 25, Issue 6 1170-1176, Copyright © 1997 by Oxford University Press
JP Cai, H Kawate, K Ihara, H Yakushiji, Y Nakabeppu, T Tsuzuki and M Sekiguchi
8-Oxo-7,8-dihydro-2'-deoxyguanosine 5'-triphosphate (8-oxo-dGTP) is
produced during normal cellular metabolism, and incorporation into DNA
causes transversion mutation. Organisms possess an enzyme, 8-oxo- dGTPase,
which catalyzes the hydrolysis of 8-oxo-dGTP to the corresponding
nucleoside monophosphate, thereby preventing the occurrence of mutation.
There are highly conserved amino acid sequences in prokaryotic and
eukaryotic proteins containing this and related enzyme activities. To
elucidate the significance of the conserved sequence, amino acid
substitutions were introduced by site- directed mutagenesis of the cloned
cDNA for human 8-oxo-dGTPase, and the activity and stability of mutant
forms of the enzyme were examined. When lysine-38 was replaced by other
amino acids, all of the mutants isolated carried the 8-oxo-dGTPase-negative
phenotype. 8-Oxo-dGTPase- positive revertants, isolated from one of the
negative mutants, carried the codon for lysine. Using the same procedure,
the analysis was extended to other residues within the conserved sequence.
At the glutamic acid-43, arginine-51 and glutamic acid-52 sites, all the
positive revertants isolated carried codons for amino acids identical to
those of the wild type protein. We propose that Lys-38, Glu-43, Arg- 51 and
Glu-52 residues in the conserved region are essential to exert 8-
oxo-dGTPase activity.
ARTICLES
Significance of the conserved amino acid sequence for human MTH1 protein with antimutator activity
Department of Biochemistry, Medical Institute of Bioregulation, Kyushu University, Fukuoka 812-82, Japan.
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