E3 ubiquitin-protein ligase that cooperates with the microRNAs (miRNAs) machinery and promotes embryonic stem cells proliferation and maintenance (Probable). Binds to miRNAs and associates with AGO2, participating in post-transcriptional repression of transcripts such as CDKN1A (By similarity). In addition, participates in post-transcriptional mRNA repression in a miRNA independent mechanism (PubMed:23125361). Facilitates the G1-S transition to promote rapid embryonic stem cell self-renewal by repressing CDKN1A expression. Required to maintain proliferation and prevent premature differentiation of neural progenitor cells during early neural development: positively regulates FGF signaling by controlling the stability of SHCBP1 (By similarity). Specific regulator of miRNA biogenesis. Binds to miRNA MIR29A hairpin and postranscriptionally modulates MIR29A levels, which indirectly regulates TET proteins expression (PubMed:28431233). {ECO:0000250|UniProtKB:Q1PSW8, ECO:0000269|PubMed:23125361, ECO:0000269|PubMed:28431233, ECO:0000305|PubMed:24239284}. This is the function of ENSG00000206557 (TRIM71, tripartite motif containing 71).