The Bacillus subtilis RNase P holoenzyme contains two RNase P RNA and two RNase P protein subunits

Ribonuclease P (RNase P) catalyzes the 5' maturation of precursor tRNA tran scripts and, in bacteria, is composed of a catalytic RNA and a protein, We investigated the oligomerization state and the shape of the RNA alone and t he holoenzyme of Bacillus subtilis RNase P in the absence of substrate by s ynchrotron small-angle X-ray scattering and affinity retention. The B, subt ilis RNase P RNA alone is a monomer; however, the scattering profile change s upon the addition of monovalent ions, possibly suggesting different inter domain angles, To our surprise, the X-ray scattering data combined with the affinity retention results indicate that the holoenzyme contains two RNase P RNA and two RNase P protein molecules. We propose a structural model of the holoenzyme with a symmetrical arrangement of the two RNA subunits, cons istent with the X-ray scattering results, This (P RNA)(2)(P protein)(2) com plex likely binds substrate differently than the conventional (P RNA)(1)(P protein)(1) complex; therefore, the function of the B. subtilis RNase P hol oenzyme may be more diverse than previously thought. These revisions to our knowledge of the RNase P holoenzyme suggest a more versatile role for prot eins in ribonucleoprotein complexes.