Key result
Rpp29 and C5 protein exhibit comparable binding affinities to precursor tRNA but different catalytic efficiencies in activating M1 RNA, with high substrate concentrations impeding Rpp29 activity.
Distinct protein folds in unrelated protein cofactors (C5 and Rpp29) can facilitate the transition from RNA- to ribonucleoprotein-based catalysis by RNase P.
Supports convergent evolution of RNase P cofactors; leaves open physiological roles in mammalian systems.
The Escherichia coli ribonuclease P (RNase P) has a protein component, termed C5, which acts as a cofactor for the catalytic M1 RNA subunit that processes the 5' leader sequence of precursor tRNA. Rpp29, a conserved protein subunit of human RNase P, can substitute for C5 protein in reconstitution assays of M1 RNA activity. To better understand the role of the former protein, we compare the mode of action of Rpp29 to that of the C5 protein in activation of M1 RNA. Enzyme kinetic analyses reveal that complexes of M1 RNA-Rpp29 and M1 RNA-C5 exhibit comparable binding affinities to precursor tRNA but different catalytic efficiencies. High concentrations of substrate impede the activity of the former complex. Rpp29 itself exhibits high affinity in substrate binding, which seems to reduce the catalytic efficiency of the reconstituted ribonucleoprotein. Rpp29 has a conserved C-terminal domain with an Sm-like fold that mediates interaction with M1 RNA and precursor tRNA and can activate M1 RNA. The results suggest that distinct protein folds in two unrelated protein cofactors can facilitate transition from RNA- to ribonucleoprotein-based catalysis by RNase P.
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E. Sharin (2005) studied this question. Rpp29 vs. C5 protein was evaluated on Activation of M1 RNA and catalytic efficiency. Rpp29 and C5 protein exhibit comparable binding affinities to precursor tRNA but different catalytic efficiencies in activating M1 RNA, with high substrate concentrations impeding Rpp29 activity.
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