Multiple antimutagenesis mechanisms affect mutagenic activity and specificity of the base analog 6-N-hydroxylaminopurine in bacteria and yeast

Cloning, Expression, and Characterization of a Human Inosine Triphosphate Pyrophosphatase Encoded by the ITPAGene

“…Overexpression of HAM1 can protect E. coli from both the toxic and mutagenic effects of HAP (21). Therefore, Ham1p must be acting as a HAP triphosphate pyrophosphatase to prevent the incorporation of HAP into DNA (20). Given the possibility that HAP could be generated inside living cells (48) and induce mutations and chromosomal aberrations (49), a role for the ITPA family in the prevention of HAP-induced mutagenesis must be considered.…”

“…This yeast protein is homologous to the Mj0226 protein, with about 30% sequence identity. Experiments with yeast HAM1 Ϫ mutants have shown that adenine-requiring haploid strains are unable to grow on HAP as the sole adenine source (19,20), whereas Escherichia coli transformed with the HAMI gene are resistant to HAP mutagenesis (21). This phenomenon presumably occurs because the conversion of HAP to HAP triphosphate and subsequent incorporation into DNA is lethal (20).…”

“…Experiments with yeast HAM1 Ϫ mutants have shown that adenine-requiring haploid strains are unable to grow on HAP as the sole adenine source (19,20), whereas Escherichia coli transformed with the HAMI gene are resistant to HAP mutagenesis (21). This phenomenon presumably occurs because the conversion of HAP to HAP triphosphate and subsequent incorporation into DNA is lethal (20). Based on biochemical information and sequence similarity, these two proteins may be microbial ITP hydrolases that can convert mutagenic, non-canonical purine nucleoside triphosphates to monophosphates and thus protect DNA from the incorporation of modified purine bases.…”

Molybdenum cofactor-dependent resistance to N-hydroxylated base analogs in Escherichia coli is independent of MobA function

“…Examples of these agents include 6-N-hydroxylaminopurine (HAP), 2-amino-6-hydroxyaminopurine (AHAP), and N 4 -hydroxycytidine. Notably HAP, an adenine analog in which the exocyclic amino group is replaced by a hydroxylamino group, has been found to be a highly effective mutagen in bacteria, yeast, and mammalian cells [3][4][5].…”

“…In yeast, drastically enhanced sensitivity to the mutagenic and toxic action of HAP was observed in ham1 mutants [6,7]. Ham1p is a specific pyrophosphatase that hydrolyzes HAP deoxyribonucleoside triphosphate to the corresponding mononucleotide, thus preventing incorporation of the analog into DNA [4,8]. While E. coli contains a homolog for the HAM1 gene, named rdgB [9,10], this system apparently plays a back-up role in HAP detoxification [11,12].…”