E3 ubiquitin-protein ligase that cooperates with the microRNAs (miRNAs) machinery and promotes embryonic stem cells proliferation and maintenance. Binds to miRNAs and participates in post-transcriptional repression of transcripts. Required to maintain proliferation and prevent premature differentiation of neural progenitor cells during early neural development. 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. 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. Belongs to the TRIM/RBCC family.