MOLECULAR ANALYSIS OF MUTATIONS INDUCED AT THE HISD3052 ALLELE OF SALMONELLA BY SINGLE CHEMICALS AND COMPLEX-MIXTURES

More single chemicals and complex environmental mixtures have been eva luated for mutagenicity at the hisD3052 allele of Salmonella, primaril y in strain TA98, than in any other mutation assay. The development of colony probe hybridization procedures and the application of the poly merase chain reaction and direct DNA sequencing has permitted rapid mo lecular access to this allele. We discuss these techniques and the res ulting mutation spectra that have been induced by a variety of environ mental mutagens and complex mixtures. A common GC or CG deletion withi n a hot-spot region of the sequence dominates most of the spectra. In addition to this two-base deletion, we have recovered about 200 other types of mutations within the 72-base target for reversion of the hisD 3052 allele. These include a variety of deletions (as large as 35 base s), duplications (as large as 46 bases), and complex mutations involvi ng base substitutions. The quasipalindromic nature of the target seque nce and its potential to form DNA secondary structures and slippage mi smatches appear to be an important basis for the mutability of this al lele.