The csrA gene encodes a global regulatory protein which facilitates glgC mRNA decay in vivo. A purified recombinant CsrA protein was found to inhibit in vitro glg (glycogen biosynthesis) gene expression posttranscriptionally and bind specifically to a glgC runoff transcript without causing its decay. Our results provide further insight into the mechanism by which CsrA functions as an mRNA decay factor.