RNA-binding protein that inhibits processing of pre-let-7 miRNAs and regulates translation of mRNAs that control developmental timing, pluripotency and metabolism. Seems to recognize a common structural G-quartet (G4) feature in its miRNA and mRNA targets (By similarity). 'Translational enhancer' that drives specific mRNAs to polysomes and increases the efficiency of protein synthesis. Its association with the translational machinery and target mRNAs results in an increased number of initiation events per molecule of mRNA and, indirectly, in mRNA stabilization. Suppressor of microRNA (miRNA) biogenesis, including that of let-7. Binds specific target miRNA precursors (pre-miRNAs), recognizing an 5'-GGAG-3' motif found in their terminal loop, and recruits uridylyltransferase. This results in the terminal uridylation of target pre-miRNAs. Uridylated pre-miRNAs fail to be processed by Dicer and undergo degradation (By similarity). Localized to the periendoplasmic reticulum area, binds to a large number of spliced mRNAs and inhibits the translation of mRNAs destined for the ER, reducing the synthesis of transmembrane proteins, ER or Golgi lumen proteins, and secretory proteins. Binds to and enhances the translation of mRNAs for several metabolic enzymes, increasing glycolysis and oxidative phosphorylation. Which, with the let-7 repression may enhance tissue repair in adult tissue (By similarity). Monomer. Predominantly cytoplasmic. In the cytoplasm, localizes to peri-endoplasmic reticulum regions and may be bound to the cytosolic surface of rough endoplasmic reticulum (ER) on which ER-associated mRNAs are translated. Shuttle from the nucleus to the cytoplasm requires RNA-binding. Expressed from mid-gastrula to the tadpole stage. Appears to be largely absent from terminally differentiated cells of the adult. The CCHC zinc fingers interact with the GGAG motif at the 3' end of let-7 miRNAs precursors, more generally they bind the 5'-NGNNG-3' consensus motif with micromolar affinity. The CSD domain recognizes the loop at the 5' end. The flexible linker allows accommodating variable sequences and lengths among let-7 family members (By similarity). Belongs to the lin-28 family.