Although archaeal RNase P RNAs are similar in both sequence
and structure to those of Bacteria rather than eukaryotes, and
heterologous reconstitution between the Bacillus subtilis
RNase P protein and some archaeal RNase P RNAs has been
demonstrated, no archaeal protein sequences with similarity
to any known bacterial RNase P protein subunit have been
identified, and the density of Methanothermobacter
thermoautotrophicus RNase P in Cs2SO4
(1.42 g/mL) is inconsistent with a single small bacterial-like
protein subunit. Four hypothetical open reading frames (MTH11,
MTH687, MTH688, and MTH1618) were identified in the genome of
M. thermoautotrophicus that have sequence similarity
to four of the nine Saccharomyces cerevisiae RNase
P protein subunits: Pop4p, Pop5p, Rpp1p, and Rpr2p, respectively.
Polyclonal antisera generated to recombinant Mth11p, Mth687p,
Mth688p, and Mth1618p each recognized a protein of the predicted
molecular weight in western blots of partially purified M.
thermoautotrophicus RNase P, and immunoprecipitated RNase
P activity from the same partially purified preparation. RNase
P in Archaea is therefore composed of an RNA subunit similar
to bacterial RNase P RNA and multiple protein subunits similar
to those in the eukaryotic nucleus.