A paralog of Pcc1 is the fifth core subunit of KEOPS complex in Archaea

In Archaea and Eukaryotes, the synthesis of a universal tRNA modification, t6A, is catalyzed by the KEOPS complex composed of Kae1, Bud32, Cgi121 and Pcc1. A fifth subunit, Gon7, is found only in Fungi and Metazoa. Mutations in all five genes encoding human KEOPS subunits leads to Galloway-Mowat syndrome, a severe genetic disease causing childhood lethality. Here, we describe the discovery and biochemical characterization of the archaeal fifth KEOPS subunit. This protein, dubbed Pcc2, is a paralog of Pcc1 and is widely conserved in Archaea. Pcc1 and Pcc2 form a heterodimer in solution, show modest sequence conservation but very high structural similarity. The 5-subunit KEOPS lost its capacity to form dimers but its tRNA binding and t6A synthetic activity remained robust. Pcc2 can substitute Pcc1 but the resulting KEOPS complex is inactive suggesting a distinct function for the two paralogs. Comparative sequence and structure analyses point to a possible evolutionary link between archaeal Pcc2 and eukaryotic Gon7 proteins. Our work thus reveals that Pcc2 has evolved to regulate the oligomeric state of KEOPS complex thus adding another layer of complexity to the biosynthesis of t6A that seems to be conserved from Archaea to Eukaryotes. ### Competing Interest Statement The authors have declared no competing interest.