A novel method for detection and characterization of ochere suppressors in Escherichia coli

Summary We have found a new method for specifically detecting the occurrence of ochre (UAA) suppression in Escherichia coli. It is based on a procedure we used several years ago to distinguish trpA missense mutants from nonsense mutants, and relies on the generally low efficiency of suppression that seems to be characteristic of ochre suppressors in E. coli. Suppressed ochre mutants are distinguishable from trpA revertants by their inability to grow on glucose minimal medium containing a low concentration (1.5 m/ml) of indole and a high concentration (50 g/ml) of 5-methyl-DL-tryptophan (Ind-5MT). The procedure provides a specific and rapid means for detection of UAA derived from missense codons and has also been exploited to obtain different classes of ochre suppressors derived from the amber suppressor supDam and from a glycine tRNA missense suppressor. The Ind-5MT phenotype seems to depend in some way on the location of the ochre codon within the trpA messenger RNA. The method can be put to many uses and should be generally applicable to all low-efficiency nonsense suppressors, including those specific for UAG and UGA.Preliminary reports of portions of this work were presented at the spring meeting of the Texas Branch of the American Society for Microbiology, College Station, Texas, March, 1975