RNA-binding protein that inhibits processing of pre-let-7 miRNAs and regulates translation of mRNAs that control developmental timing, pluripotency and metabolism (PubMed:21247876). Seems to recognize a common structural G-quartet (G4) feature in its miRNA and mRNA targets (Probable). '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. Binds IGF2 mRNA, MYOD1 mRNA, ARBP/36B4 ribosomal protein mRNA and its own mRNA. Essential for skeletal muscle differentiation program through the translational up-regulation of IGF2 expression. Suppressor of microRNA (miRNA) biogenesis, including that of let-7, miR107, miR-143 and miR-200c. Specifically binds the miRNA precursors (pre-miRNAs), recognizing an 5'-GGAG-3' motif found in pre-miRNA terminal loop, and recruits TUT4 and TUT7 uridylyltransferases (PubMed:18951094, PubMed:19703396, PubMed:22118463, PubMed:22898984). This results in the terminal uridylation of target pre-miRNAs (PubMed:18951094, PubMed:19703396, PubMed:22118463, PubMed:22898984). Uridylated pre-miRNAs fail to be processed by Dicer and undergo degradation. The repression of let-7 expression is required for normal development and contributes to maintain the pluripotent state by preventing let-7-mediated differentiation of embryonic stem cells (PubMed:18951094, PubMed:19703396, PubMed:22118463, PubMed:22898984). 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, such as PFKP, PDHA1 or SDHA, increasing glycolysis and oxidative phosphorylation. Which, with the let-7 repression may enhance tissue repair in adult tissue (By similarity). Monomer (By similarity). During skeletal muscle differentiation, associated with translation initiation complexes in the polysomal compartment (PubMed:21247876). Directly interacts with EIF3S2 (By similarity). Interacts with NCL in an RNA-dependent manner (By similarity). Interacts (via C-terminus) with DHX9 (via N- and C-terminus); this interaction occurs in a RNA-independent manner (PubMed:21247876). Interacts with TUT4 in the presence of pre-let-7 RNA (PubMed:19703396, PubMed:22118463). Predominantly cytoplasmic (PubMed:22118463). In the cytoplasm, localizes to peri-endoplasmic reticulum regions and detected in the microsomal fraction derived from rough endoplasmic reticulum (RER) following subcellular fractionation. May be bound to the cytosolic surface of RER on which ER-associated mRNAs are translated (By similarity). Shuttle from the nucleus to the cytoplasm requires RNA-binding (PubMed:17617744). Nucleolar localization is observed in 10-15% of the nuclei in differentiated myotubes (By similarity). Expressed in embryonic stem cells, placenta and testis. Tends to be up-regulated in HER2-overexpressing breast tumors. Expressed in fetal liver. Expression decreases during differentiation of ES cells or upon induction of neuronal differentiation by retinoic acid. Can be negatively regulated by the interaction of microRNAs miR-125a and miR-125b with at least two miRNA responsive elements (miREs) in the 3'-UTR of this gene. These interactions may reduce both translation efficiency and mRNA abundance. Negatively regulated by retinoic acid. The CSD domain is required for function in muscle differentiation. 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. Overexpressed in primary tumors (overall frequency approximately 15%), overexpression being linked to repression of let-7 family miRNAs and derepression of let-7 targets. Facilitates cellular transformation in vitro, and overexpression is associated with advanced disease across multiple tumor types. Reactivation of LIN28A expression enhances tissue repair in some adult tissues by reprogramming cellular bioenergetics. Improves hair regrowth by promoting anagen in hair follicle and accelerates regrowth of cartilage, bone and mesenchyme after ear and digit injuries. Belongs to the lin-28 family.