This domain can be found in Kae1/Qri7/YgjD, products of COG0533 that belong to a small group of 60 proteins that are present in all three domains of life. COG0533 proteins are suggest to play a role in a post translational modification of certain tRNAs. For example, YgjD along with YeaZ, YjeE, and YrdC have been deemed necessary and sufficient for the tRNA modification [1]. This modification involves the formation of N6-threonyl carbamoyl adenosine (t6A) at position 37 in the anti-codon stem loop which is critical for translational speed and accuracy [2]. Structural analysis indicate that YeaZ lacks resemblance to any known protease active site. Together with the absence of a putative zinc-binding motif. Thus the likelyhood of it being a protease, as previously thought, has been negated [1]. EC:2.3.1.234

1: Crystal structure of the dimer of two essential Salmonella typhimurium proteins, YgjD & YeaZ and calorimetric evidence for the formation of a ternary YgjD-YeaZ-YjeE complex. Nichols CE, Lamb HK, Thompson P, El Omari K, Lockyer M, Charles I, Hawkins AR, Stammers DK; Protein Sci. 2013;22:628-640. PMID:23471679

2: Global translational impacts of the loss of the tRNA modification t(6)A in yeast. Thiaville PC, Legendre R, Rojas-Benitez D, Baudin-Baillieu A, Hatin I, Chalancon G, Glavic A, Namy O, de Crecy-Lagard V; Microb Cell. 2016;3:29-45. PMID:26798630