Rapid selection of nonhotspot mutants among hisD+ revertants of Salmonella typhimurium TA98 in Ames test by peptide nucleic acid (PNA)-mediated PCR clamping.

Ames test is the most popular method of assessing mutagenicity using Salmonella typhimurium as an indicator. Recently, sequence analyses have been introduced for the investigation of mutation mechanisms. Most revertants (>70%) carry 2-bp deletion within an 8-bp CG repeat in hisD (hotspot mutation) in the Ames test using S. typhimurium TA98. We developed a new specific amplification method for nonhotspot mutants by peptide nucleic acid (PNA)-mediated PCR clamping. It markedly reduces the labor and cost of this kind of studies.