Cellular innate immune sensors detect foreign signals emanating from pathogens. Nallagatla et al. report that the pivotal sensing protein, double-stranded RNA-activated protein kinase (PKR), is finely tuned to recognize the 5′-triphosphate structures of single-stranded RNA molecules present in many bacteria and viruses. This recognition strategy is similar to the recently described detection of nucleic acid 5′-end signatures by another sensing protein, RIG-I. It remains unclear exactly how these key sensors go on to tailor the most appropriate cellular responses to intracellular pathogens.
S. R. Nallagatla, J. Hwang, R. Toroney, X. Zheng, C. E. Cameron, P. C. Bevilacqua, 5′-triphosphate-dependent activation of PKR by RNAs with short stem-loops. Science 318, 1455-1458 (2007). [Abstract] [Full Text]