SILENT MUTATIONS IN THE ESCHERICHIA-COLI OMPA LEADER PEPTIDE REGION STRONGLY AFFECT TRANSCRIPTION AND TRANSLATION IN-VIVO

In order to test the effect of silent mutations on the regulation of g ene expression, we monitored several steps of transcription and transl ation of the ompA gene in vivo, in which some or all codons between co dons 6 and 14, frequently used in Escherichia coil, had been exchanged for infrequent synonymous codons. Northern blot analysis revealed an up to 4-fold reduction in the half-life of the mutated messengers and a >10-fold reduction in their steady-state amounts. Western blot analy sis showed a 10-fold reduction in the amount of OmpA protein. Use of a system expressing a Rho-specific anti-terminator allowed us to detect a strong transcription polarity effect in the silent mutants. These r esults demonstrate that silent mutations can severely inhibit several steps of gene expression in E. coli and that code degeneracy is effici ently exploited in this species for setting signals for gene control a nd regulation.