Separation of the COG009 family into two subgroups YrdC and YciO based on motifs and functional assays. (A) Complementation of the t6A- phenotype of the yeast Δsua5 (YGN63) strain by the E. coli yrdC gene but not the E. coli yciO gene. (B) Complementation of the yrdC essentiality phenotype in E. coli by yrdC subfamily members from E .coli (EcyrdC), Bacillus subtilis (BsywlC), Methanococcus maripaludis (MmyrdC) and yeast (Scsua5) but not by yciO from E. coli (EcyciO). All genes were cloned in pBAD24  and were therefore expressed in the presence of arabinose (Ara, 0.2%) and transformed in an E.coli strain carrying the chromosomal copy of yrdC under PTet control  that does not grow in the absence of anhydrotetracycline (ATc, 50 ng/ml). (C) Signature motif of the functional homologs of YrdC (KxR/SxN) that are not found in the YciO subfamily. In green are the two homologs from Arabidopsis and their distribution.