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. Author manuscript; available in PMC: 2020 May 11.
Published in final edited form as: Adv Biol Regul. 2016 Sep 26;63:167–176. doi: 10.1016/j.jbior.2016.09.008

Fig. 3. Model for Fhit as a scavenger decapping enzyme regulating translation of TK1 mRNA.

Fig. 3.

A) Structure of diadenosine triphosphate (Ap3A), the first recognized in vitro substrate for Fhit, and the 5’ 7-methyl-guanosine cap. B) In the 3‟ to 5‟ mRNA decay pathway, the exosome generates free m7GpppN dinucleotides that can be hydrolyzed by a scavenger decapping enzyme. The model hypothesizes that In the presence of Fhit, Fhit binds and hydrolyzes m7GpppN into m7GDP and m7GMP, which are cleared from the cell. In the absence of Fhit, free m7GpppN caps accumulate. Preferential binding of translation initiation factors to these free caps instead of capped TK1 mRNAs leads to deregulated translation of TK1 mRNA. As the model proposes, Fhit is thus a scavenger-decapping enzyme that eliminates residual cap structures to promote ribosomal binding and translation of cap-bearing mRNAs.