Structural basis for the CsrA-dependent modulation of translation initiation by an ancient regulatory protein

Proc Natl Acad Sci U S A.           online article

CsrA proteins are repressors of translation that target the Shine–Dalgarno sequence. Small noncoding RNAs competitively sequester CsrA by offering multiple binding sites that mimic the S–D. Antagonism of CsrA by small nc RNAs is a widely conserved mechanism of posttranscriptional regulation. We present the first crystal structure of FliW, which allosterically regulates CsrA in specific manner. Our phylogenetic analysis reveals that the FliW–CsrA regulon is subject to coevolution and represents the ancestral state of flagellated bacteria.