A hairpin structure upstream of the terminator hairpin required for ribosomal protein L4-mediated attenuation control of the S10 operon of Escherichia coli.

Ribosomal protein L4 of Escherichia coli regulates transcription of the 11-gene S1O operon by promoting premature termination of transcription (attenuation) at a specific site within the 172-base untranslated leader. We have analyzed the roles of various domains of the leader RNA in this transcription control. Our results indicate that the first 60 bases of the leader, forming the three proximal hairpin structures, are not essential for in vivo L4-mediated attenuation control. However, a deletion removing the fourth hairpin, which is immediately upstream of the terminator hairpin, eliminates L4's effect on transcription. Base changes disrupting complementarity in the 6-bp stem of this hairpin also abolish L4 control, but compensatory base changes that restore complementarity also restore L4's effect. In vitro transcription studies confirm that this hairpin structure is necessary for L4's role in stimulating transcription termination by RNA polymerase.