Point mutations that affect translation initiation of the transposon Tn10 tetA gene.

Single base-pair changes affecting the 5' untranslated leader of the tetracycline-resistance gene (tetA) mRNA resulted in increased or decreased levels in expression of tetA-lacZ protein fusions. The base changes affected the rate of initiation of translation of tetA mRNA because operon fusions revealed that the mutations had little or no effect on transcription. The translational efficiency of wild-type and mutant tetA mRNAs varied by more than a factor of 2000. The observed variations could be correlated with stabilization and destabilization of RNA secondary structures. These structures, located 5' from the translation start codon, sequester the Shine-Dalgarno sequence.