E3 ubiquitin-protein ligase that cooperates with the microRNAs (miRNAs) machinery and promotes embryonic stem cells proliferation and maintenance (By similarity). 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 (By similarity). 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 (By similarity). S-ubiquitinyl-[E2 ubiquitin-conjugating enzyme]-L-cysteine + [acceptor protein]-L-lysine = [E2 ubiquitin-conjugating enzyme]-L-cysteine + N(6)-ubiquitinyl-[acceptor protein]-L-lysine. Protein modification; protein ubiquitination. Interacts (via NHL repeats) with AGO2; the interaction increases in presence of RNA. Interacts with HSP90AA1. Interacts (via NHL repeats) with MOV10, PABPC1, PUM1, PUM2, STAU2, XRN1 and XRN2 in an RNA-dependent manner (By similarity). Interacts with SHCBP1; leading to enhance its stability (By similarity). The NHL domain, containing the 6 NHL repeats, is necessary and sufficient to target RNA but not to repress mRNA. The minimal region needed to execute repression consists of the coiled coil domain and the Filamin repeat. The RING-type domain is dispensable for mRNA repression. Autoubiquitinated. Belongs to the TRIM/RBCC family.