Protein lin-28 homolog B (Lin28b)

Suppressor of microRNA (miRNA) biogenesis, including that of let-7 and maybe of miR107, miR-143 and miR-200c. Binds primary let-7 transcripts (pri-let-7), including pri-let-7g and pri-let-7a-1, and sequester them in the nucleolus, away in the microprocessor complex, hence preventing their processing into mature miRNA.

Does not act on pri-miR21. The repression of let-7 expression is required for normal development and contributes to keep the pluripotent state of embryonic stem cells by preventing let-7-mediated differentiation.