Journal
CHEMBIOCHEM
Volume 13, Issue 15, Pages 2270-2276Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/cbic.201200434
Keywords
catalytic mechanisms; kinetics; PRORP; proteinaceous RNase P; Rp-phosphorothioate modifications
Funding
- Deutsche Forschungsgemeinschaft [HA 1672/17-1]
- Austrian Science Fund FWF [I299]
- Austrian Science Fund (FWF) [I299, W1207] Funding Source: Austrian Science Fund (FWF)
- Austrian Science Fund (FWF) [I 299] Funding Source: researchfish
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In Arabidopsis thaliana, RNase P function, that is, endonucleolytic tRNA 5'-end maturation, is carried out by three homologous polypeptides (proteinaceous RNase P (PRORP) 1, 2 and 3). Here we present the first kinetic analysis of these enzymes. For PRORP1, a specificity constant (kreact/Km(sto)) of 3 X 106 M-1min-1 was determined under single-turnover conditions. We demonstrate a fundamentally different sensitivity of PRORP enzymes to an Rp-phosphorothioate modification at the canonical cleavage site in a 5'-precursor tRNA substrate; whereas processing by bacterial RNase P is inhibited by three orders of magnitude in the presence of this sulfur substitution and Mg2+ as the metal-ion cofactor, the PRORP enzymes are affected by not more than a factor of five under the same conditions, without significantly increased miscleavage. These findings indicate that the catalytic mechanism utilized by proteinaceous RNase P is different from that of RNA-based bacterial RNase P, taking place without a direct metal-ion coordination to the (pro-)Rp substituent. As Rp-phosphorothioate and inosine modification at all 26 G residues of the tRNA body had only minor effects on processing by PRORP, we conclude that productive PRORPsubstrate interaction is not critically dependent on any of the affected (pro-)Rp oxygens or guanosine 2-amino groups.
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