title: Mutagen specificity and position effects on mutation in T4rII nonsense sites.
abstract: In 14 sites in the T4rII region, spontaneous and induced interconversions of ochre (UAA) and opal (UGA) alleles, as well as the reversion of the nonsense sites to r+, were studied. The mutagens employed were 2-aminopurine (2AP), 5-bromouracil (5BU), N-methyl-N'-nitro-N-nitrosoguanidine (NTG) and hydroxylamine (HA). With the test system employed, mutagen specificity (i.e., the preferential induction of A: T  leads to G: C or G: C leads to A: T mutation at a given site) can be studied. Simultaneously, the response of similar base pairs at various locations in the same or in different nucleotide triplets throughout the rII region, to a given mutagen, can be compared. 2-Aminopurine can induce transitions of both A: T and G: C base pairs at high rates. This mutagen shows no preference for either direction. Furthermore, there is a correlation between the response to 2AP of an A: T pair occupying a given site, and that of a G: C pair occupying the same site. NTG and HA induce G: C leads to A: T transitions almost exclusively. However, there is a correlation between the low rates of A: T leads to G: C transition induced in each of the various sites by these mutagens and those of G: C leads to A: T. 5-Bromouracil induces transitions from G: C to A: T more readily than from A: T to G: C. With 5BU-induced mutation, there is no correlation between the rates of G: C leads to A: T transitions and those of A: T leads to G: C. In UAA sites, all three adenine:thymidine paris respond to 2AP mutagenesis in a similar pattern, In each position in the triplet, response to 2 AP is correlated with that to 5BU. In UGA sites, there are correlations among the spontaneous as well as the 2AP-, HA- and NTG-induced transition rates. 5BU-induced transition rates are usually not correlated with those induced by other mutagens or with the sponatneous ones.
mesh_terms: D015075:2-Aminopurine / Q000494:pharmacology; D000483:Alleles; D001483:Base Sequence; D001976:Bromouracil / Q000494:pharmacology; D003062:Codon; D003090:Coliphages / Q000378:metabolism*; D004279:DNA, Viral; D005796:Genes; D006898:Hydroxylamines / Q000494:pharmacology; D008769:Methylnitronitrosoguanidine / Q000494:pharmacology; D009154:Mutation; D014764:Viral Proteins
chemical_list: D003062:Codon; D004279:DNA, Viral; D006898:Hydroxylamines; D014764:Viral Proteins; D008769:Methylnitronitrosoguanidine; D015075:2-Aminopurine; D001976:Bromouracil