Minimal and RNA-free RNase P in Aquifex aeolicus

Significance RNase P is a tRNA-processing enzyme of unique architectural diversity: either a catalytic RNA plus one or more (up to 10) proteins, or one (or three) unrelated proteins only. We identified yet another enzyme form in the bacterium Aquifex aeolicus , a 23-kDa protein and the smallest known form of RNase P. Apparently, it was acquired by horizontal gene transfer from Archaea. In some other bacteria and many archaea, it is simultaneously present with the presumably more ancient RNA-based enzyme form. Bacteria with both activities may represent the missing link of RNase P evolution, a transition state that had also been once traversed by the Aquificaceae , which, however, later lost their RNA-based RNase P.