Dynamic refolding of IFN-gamma mRNA enables it to function as PKR activator and translation template.
Interferon-gamma mRNA activates the RNA-dependent protein kinase PKR, which in turn strongly attenuates translation of interferon-gamma mRNA. Unlike riboswitches restricted to noncoding regions, the interferon-gamma RNA domain that activates PKR comprises the 5' UTR and 26 translated codons. Extensive interferon-gamma coding sequence is thus dedicated to activating PKR and blocking interferon-gamma 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-gamma mRNA, which is necessary for its dual function as translation template and activator of PKR, and which thus prevents overexpression of this inflammatory cytokine.
Department of Biochemistry and Molecular Biology, Institute for Medical Research Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem, Israel.
Smadar
S
Cohen-Chalamish
Anat
A
Hasson
Dahlia
D
Weinberg
Lise Sarah
LS
Namer
Yona
Y
Banai
Farhat
F
Osman
Raymond
R
Kaempfer
D020121:5' Untranslated Regions; D000818:Animals; D001483:Base Sequence; D004789:Enzyme Activation; D006801:Humans; D007371:Interferon-gamma / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D014176:Protein Biosynthesis; D017510:Protein Folding; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism*; D013698:Templates, Genetic; D019892:eIF-2 Kinase / Q000235:genetics / Q000378:metabolism*
D020121:5' Untranslated Regions; D012333:RNA, Messenger; D007371:Interferon-gamma; D019892:eIF-2 Kinase