Involved in the final steps of cytoplasmic maturation of the 40S ribosomal subunit. Involved in processing of 18S-E pre-rRNA to the mature 18S rRNA. Required for the recycling of NOB1 and PNO1 from the late 40S precursor (By similarity). The association with the very late 40S subunit intermediate may involve a translation-like checkpoint point cycle preceeding the binding to the 60S ribosomal subunit (By similarity). Despite the protein kinase domain is proposed to act predominantly as an ATPase (By similarity). The catalytic activity regulates its dynamic association with the 40S subunit (By similarity). In addition to its role in ribosomal biogenesis acts as an adapter protein by recruiting NCL/nucleolin the to PRMT5 complex for its symmetrical methylation (By similarity). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Associates with the precursor of the 40S ribosome subunit. Interacts (via its N-terminus) with PRMT5 (via its N-terminus). Interacts with WDR77 (By similarity). Found in a PRMT5 complex composed of PRMT5, WDR77 and RIOK1 (By similarity). Interacts (via its C-terminus) with NCL; this interaction targets NCL for PRTM5 methylation (By similarity). Belongs to the protein kinase superfamily. RIO-type Ser/Thr kinase family. Truncated N-terminus. Intron retention.