New polarity suppressors in Escherichia coli: suppression and messenger RNA stability

Two new polarity suppressors (Su27 and Su78) have been isolated in Escherichia coli. Both suppress polarity in the trp and lac operons, and neither shows codon specificity for suppression. Extreme polar mutants of the lac z gene that contain either Su27 or Su78 make mRNA from the entire operon; however, no active beta-galactosidase is translated from the z-gene messenger, and the amount of distal messenger is greater than would be expected from corresponding enzyme activities. Puromycin treatment of lac(+) strains mimics the effect of polar chain-termination mutations in destabilizing lac mRNA. This effect is completely reversed by Su27, and it is partially reversed by Su78. The results suggest that these suppressors act by stabilizing mRNA after premature termination of protein synthesis.