Description
RIOK1, also known as RIO kinase 1, is a member of the RIO family of atypical serine protein kinases first characterized in yeast. RIOK1 and RIOK2 proteins are present in organisms from Archaea to humans. RIOK1 functions as a new interactor of protein arginine methyltransferase 5 (PRMT5), competes with pICln for binding and modulates PRMT5 complex composition and substrate specificity. RioK1 and pICln bind to PRMT5 in a mutually exclusive fashion. This results in a PRMT5-WD45/MEP5 core structure that either associates with pICln or RioK1 RIOK1 in distinct complexes. RIOK1 functions in analogy to pICln as an adapter protein by recruiting the RNA-binding protein nucleolin to the PRMT5 complex for its symmetrical methylation