Ribosomal RNA processing protein 9 (RRP9)

Ribosomal RNA processing protein 9 (RRP9) is a highly conserved, nucleolar, WD-repeat protein that specifically associates with U3 small nucleolar RNA (snoRNA), forming part of the U3 snoRNP complex, which is essential for eukaryotic ribosome biogenesis[1][2][4]. RRP9 plays a key role in the early steps of precursor ribosomal RNA (pre-rRNA) processing by facilitating the cleavage events necessary for the formation of the 18S rRNA—a component of the small ribosomal subunit[1][2][3][4]. Structurally, RRP9 has a WD-repeat domain, forming a β-propeller fold involved in specific RNA and protein interactions[1][2]. RRP9 functions as a molecular scaffold in the SSU (small subunit) processome, where it specifically recognizes and binds to the U3 snoRNA via conserved motifs (notably a unique B/C box)[1][2]. Its precise association with U3 snoRNA, enhanced by interaction with the Snu13 protein, is critical for correct assembly of the U3 snoRNP complex and subsequent pre-rRNA processing[1][2][3]. Mutations in RRP9 or in U3 snoRNA disrupting this interaction lead to failure in ribosome assembly and—at least in yeast—cell lethality[1][2][3]. There is currently no evidence indicating that RRP9 is a therapeutic target, nor are there known drugs or small molecules targeting this protein. Consequently, no clinical safety concerns, mechanism-of-action details, or approved biomarkers are associated with RRP9 in a therapeutic context.

Other names

U3 small nucleolar RNA-interacting protein 2RNU3IP2U3-55KU3 snoRNP-associated 55 kDa proteinU3-55K homologU3 small nucleolar ribonucleoprotein-associated 55 kDa proteinSSU processome component homolog