cl17248

RIO kinase family, catalytic domain. 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). RIO kinases are atypical protein serine kinases present in archaea, bacteria and eukaryotes. Serine kinases catalyze the transfer of the gamma-phosphoryl group from ATP to serine residues in protein substrates. RIO kinases contain a kinase catalytic signature, but otherwise show very little sequence similarity to typical PKs. The RIO catalytic domain is truncated compared to the catalytic domains of typical PKs, with deletions of the loops responsible for substrate binding. Most organisms contain at least two RIO kinases, RIO1 and RIO2. A third protein, RIO3, is present in multicellular eukaryotes. In yeast, RIO1 and RIO2 are essential for survival. They function as non-ribosomal factors necessary for late 18S rRNA processing. RIO1 is also required for proper cell cycle progression and chromosome maintenance. The biological substrates for RIO kinases are still unknown.