tmRNA to the rescue

The molecular processes responsible for protein synthesis are usually very efficient, but the ribosomes can stall if defective or incomplete mRNA molecules dock and initiate translation. To rescue stalled ribosomes, bacteria use tmRNA (also known as 10Sa RNA), a ∼300-nucleotide-long molecule so-named for its dual tRNA-like and mRNA-like nature. Although the tmRNA structure is well known — an alanyl-tRNA like domain, an open reading frame, and four pseudoknots — its modes of action have been unclear. In the April 4 issue of Science, Mikel Valle and colleagues from the Howard Hughes Medical Institute, Albany, New York, US, present the structure of tmRNA in complex with the ribosome as determined by cryo-electron microscopy (cryo-EM), gathering important new insights into tmRNA function (Science, 300:127-130, April 4, 2003).

Valle et al. used purified Thermus thermophilus extracts and prepared a stalled ribosome with a docked tmRNA. They added the protein...