RIO kinase 2 (RIOK2) is a member of the RIO family of atypical serine protein kinases first characterized in yeast. There are three RIO kinase subfamilies: RIO1, RIO2, and RIO3. RIOK1 and RIOK2 proteins are present in organisms from Archaea to humans. Studies of RIO kinases in yeast indicate that they play a role in ribosome biogenesis. Human RIOK2 has been shown to be a part of a late 40S pre-ribosomal particle and have influence on 40S maturation.