CsrA-Mediated Translational Activation of <i>ymdA</i> Expression in Escherichia coli
Andrew Renda, Stephanie Poly, Ying-Jung Lai, Archana Pannuri, Helen Yakhnin, Anastasia H. Potts, Philip C. Bevilacqua, Tony Romeo, Paul Babitzke
Abstract
The Csr system of E. coli controls gene expression and physiology on a global scale. CsrA protein, the central component of this system, represses translation initiation of numerous genes by binding to target transcripts, thereby competing with ribosome binding. Variations of this mechanism are so common that CsrA is sometimes called a translational repressor. Although CsrA-mediated activation mechanisms have been elucidated in which bound CsrA inhibits RNA degradation, no translation activation mechanism has been defined. Here, we demonstrate that CsrA binding to two sites in the 5′ untranslated leader of ymdA mRNA activates translation by destabilizing a structure that otherwise prevents ribosome binding. The extensive role of CsrA in activating gene expression suggests the common occurrence of similar activation mechanisms.