A 2-substituted purine nucleotide analog, 2-hydroxy-2'-deoxyadenosine 
5'-triphosphate (2-OH-dATP), was added to a PCR mixture, to examine its 
mutagenic potential. The 2-OH-dATP enhanced the total mutation frequency. 
Interestingly, 2-OH-dATP induced both transition and transversion mutations, 
including A:T-->G:C, A:T-->C:G and G:C-->T:A mutations. In contrast, other 
2-substituted purine nucleotide analogs, 2-aminopurine-2'-deoxyriboside 
5'-triphosphate and 2-amino-2'-deoxyadenosine 5'-triphosphate, did not affect 
the total mutation frequency. These results suggest that 2-OH-dATP is useful in 
random PCR mutagenesis for the in vitro evolution of nucleic acids and proteins, 
and for analyses of residues in these biomolecules.