Readthrough and suppression of nonsense codons was compared in Escherichia coli strains with and without a miaA mutation, which confers a loss of the isopentenyladenosine modification in transfer RNA. Generally speaking, our results conform to predictions based on previous literature. In addition, we showed that the miaA mutation in strain TRPX is itself a UAA mutation. An antagonism between miaA and rpsL mutations, which confer streptomycin resistance, was also discovered. Our data further suggest that slight alterations of the translation apparatus are easily detectable by monitoring readthrough and suppression of nonsense codons. Our findings are discussed in the context of old and recent reports.