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Catalytic domain of the atypical protein serine kinases, RIO1 and RIO3 kinases and similar proteins RIO1 is present in archaea, bacteria and eukaryotes. In addition, RIO3 is present in multicellular eukaryotes. Both RIO1 and RIO3 are associated with precursors of 40S ribosomal subunits, just like RIO2. RIO1 is essential for survival and is required for 18S rRNA processing, proper cell cycle progression and chromosome maintenance. Although depletion of either RIO1 and RIO2 results in similar effects, the two kinases are not fully interchangeable. The specific function of RIO3 is unknown. RIO kinases are atypical protein serine kinases containing a kinase catalytic signature, but otherwise show very little sequence similarity to typical PKs. Serine kinases catalyze the transfer of the gamma-phosphoryl group from ATP to serine residues in protein substrates. The RIO catalytic domain is truncated compared to the catalytic domains of typical PKs, with deletions of the loops responsible for substrate binding. The RIO kinase catalytic domain family is part of a larger superfamily, that includes the catalytic domains of other kinases such as the typical serine/threonine/tyrosine protein kinases (PKs), aminoglycoside phosphotransferase, choline kinase, and phosphoinositide 3-kinase (PI3K). |
Jiyao W et al.(2023). "The conserved domain database in 2023.",