Minimal and RNA-free RNase P in <i>Aquifex aeolicus</i>.

Abstract

RNase P is an essential tRNA-processing enzyme in all domains of life. We identified an unknown type of protein-only RNase P in the hyperthermophilic bacterium <i>Aquifex aeolicus</i>: Without an RNA subunit and the smallest of its kind, the 23-kDa polypeptide comprises a metallonuclease domain only. The protein has RNase P activity in vitro and rescued the growth of <i>Escherichia coli</i> and <i>Saccharomyces cerevisiae</i> strains with inactivations of their more complex and larger endogenous ribonucleoprotein RNase P. Homologs of <i>Aquifex</i> RNase P (HARP) were identified in many Archaea and some Bacteria, of which all Archaea and most Bacteria also encode an RNA-based RNase P; activity of both RNase P forms from the same bacterium or archaeon could be verified in two selected cases. Bioinformatic analyses suggest that <i>A. aeolicus</i> and related <i>Aquificaceae</i> likely acquired HARP by horizontal gene transfer from an archaeon.