Dynamic refolding of IFN-g mRNA enables it to function as PKR activator and translation template

• Published in: Nature chemical biology Vol. 5; no. 12; pp. 896 - 903
• Main Authors: Cohen-Chalamish, Smadar, Hasson, Anat, Weinberg, Dahlia, Namer, Lise Sarah, Banai, Yona, Osman, Farhat, Kaempfer, Raymond
• Format: Journal Article
• Language: English
• Published: 01.12.2009
• ISSN: 1552-4450
• DOI: 10.1038/nchembio.234

Interferon-g mRNA activates the RNA-dependent protein kinase PKR, which in turn strongly attenuates translation of interferon-g mRNA. Unlike riboswitches restricted to noncoding regions, the interferon-g RNA domain that activates PKR comprises the 5' UTR and 26 translated codons. Extensive interferon-g coding sequence is thus dedicated to activating PKR and blocking interferon-g synthesis. This implies that the PKR activator is disrupted by ribosomes during translation initiation and must refold promptly to restore PKR activation. The activator structure harbors an essential kink-turn, probably to allow formation of a pseudoknot that is critical for PKR activation. Three indispensable short helices, bordered by orientation-sensitive base pairs, align with the pseudoknot stem, generating RNA helix of sufficient length to activate PKR. Through gain-of-function mutations, we show that the RNA activator can adopt alternative conformations that activate PKR. This flexibility promotes efficient refolding of interferon-g mRNA, which is necessary for its dual function as translation template and activator of PKR, and which thus prevents overexpression of this inflammatory cytokine.