February 6, 2004

Mary E. Lee, California State University, Los Angeles

Studying ssrA regulation and the post-rescue fate of tmRNA in Escherichia coli

MIT Summer Research Program, Summer 2003


Transfer-messenger RNA (tmRNA) is a unique and stable molecule highly conserved throughout bacteria. It is an integral participant in trans-translation, a process which serves to both rescue stalled ribosomes and tag their nascent proteins for proteolysis. Both the regulation of the ssrA gene (which encodes tmRNA) and the post-rescue fate of the tmRNA molecule were investigated in Escherichia coli. Precursor tmRNA levels and ssrA promoter activity are both increased in actively-rescuing cultures when compared to control groups. This implies an up-regulation of ssrA in response to a demand for ribosome rescue. To study the fate of tmRNA, its levels were monitored in cells undergoing trans-translation as functions of time after treatment with the drug rifampicin, which essentially halts all transcriptional activity. From these experiments, it appears that the mechanism for trans-translation involves cleavage or degradation of the tmRNA molecule itself.