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.
Cohen-Chalamish
Smadar
S
Department of Biochemistry and Molecular Biology, Institute for Medical Research Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem, Israel.
Hasson
Anat
A
Weinberg
Dahlia
D
Namer
Lise Sarah
LS
Banai
Yona
Y
Osman
Farhat
F
Kaempfer
Raymond
R
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