SALMONELLA-TYPHIMURIUM STRAIN TA100 DIFFERENTIATES SEVERAL CLASSES OFCARCINOGENS AND MUTAGENS BY BASE SUBSTITUTION SPECIFICITY

The mutational specificity of N-methylnitrosourea (MNU), nitrosoguanid ine (MNNG), methyl methanesulfonate (MMS), sodium azide (NaN3), 4-nitr oquinoline oxide (4NQO), benzo[a]pyrene (BP), nitrofurantoin (NF), alf atoxin B-1 (AFB(1)), adriamycin (ADM) and WA-activated angelicin in Sa lmonella typhimurium strain TA100 has been examined using allele-speci fic oligonucleotide hybridization and DNA sequence analyses. These ten mutagens produced five unique classes of reversion spectra, distinct from spontaneous, or the previously characterized 5-azacytidine, ultra violet light(UV), 8-methoxypsoralen plus UVA (PUVA) and Co-60-induced mutation spectra. For example, 90% of MNU and MNNG-induced mutations i n sh ain TA100 revertants were G:C-A:T transitions with the majority ( 82%) occurring in the first position of the CCC codon. In contrast, Na N3 preferentially induced G:C-->A:T transitions at the second codon po sition (78%). Although MMS, NQO, BP, NP, ADM and AFB(1) induced primar ily G:C-->T:A transversions (73-86%), these mutagens fall into two cla sses based on site preference: NF and AFB(1) yielded almost exclusivel y position two transversions (69-78%) whereas ADM, NQO, BP and MMS exh ibited a two-fold preference for site 2 over site 1 (on average 52% ve rsus 22%). Angelicin photomutagenesis resulted in the recovery of G:C- ->A:T and G:C-->T:A mutations at both codon positions in roughly equal proportions (similar to 20-25% each). Approximately 1% of the mutagen -induced revertants occurred via extragenic tRNA suppressor mutations, while 1% were multiple (usually tandem double) base substitutions. Ul traviolet mutagenesis experiments demonstrated that tandem base substi tutions are promoted by pKM101-encoded mucAB gene products. A comparis on of the mutagenic specificity derived for several carcinogens in his G46 with the responses of several eukaryotic gene targets (e.g. HPRT, aprt, supF) revealed a high concordance between these targets. Thus, t he Salmonella hirG46 locus provides a rapid, simple system for determi ning base substitution specificity and for studying mechanisms of muta genesis.