RNase P RNA from the recently evolved plastid of Paulinella and from algae.

Pilar Bernal-Bayard,Leonor Puerto-Galán,Agustín Vioque

doi:10.3390/ijms151120859

Pilar Bernal-Bayard, Leonor Puerto-Galán + Show 1 more

Open Access

https://doi.org/10.3390/ijms151120859

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Abstract

The RNase P RNA catalytic subunit (RPR) encoded in some plastids has been found to be functionally defective. The amoeba Paulinella chromatophora contains an organelle (chromatophore) that is derived from the recent endosymbiotic acquisition of a cyanobacterium, and therefore represents a model of the early steps in the acquisition of plastids. In contrast with plastid RPRs the chromatophore RPR retains functionality similar to the cyanobacterial enzyme. The chromatophore RPR sequence deviates from consensus at some positions but those changes allow optimal activity compared with mutated chromatophore RPR with the consensus sequence. We have analyzed additional RPR sequences identifiable in plastids and have found that it is present in all red algae and in several prasinophyte green algae. We have assayed in vitro a subset of the plastid RPRs not previously analyzed and confirm that these organelle RPRs lack RNase P activity in vitro.

Highlights

RNase P is an ubiquitous enzyme responsible for the generation of the 5'-end of tRNAs by a single endonucleolytic cleavage of 5'-extended precursors [1]
The rnpB gene was unambiguously identified in both genomes. They contain all the residues universally conserved in bacteria [25]. Both RNAs can be folded into a secondary structure similar to the cyanobacterial RNase P RNA catalytic subunit (RPR) structure (Figure 1)
We have used the specific conditions described previously to detect catalytic activity of the human RPR [37], which is six orders of magnitudes lower than the activity of E. coli RPR. These results confirm and generalize the apparent lack of RNase P activity of plastid RPRs and raise the question of what is the function of these RNAs if any in vivo, and why the rnpB genes are conserved in all red algae and several prasinophyte in spite of massive gene losses during plastid evolution

Summary

Introduction

RNase P is an ubiquitous enzyme responsible for the generation of the 5'-end of tRNAs by a single endonucleolytic cleavage of 5'-extended precursors [1]. PRORP seems to have replaced the ancestral ribonucleoprotein enzyme in the organelles of several eukaryotic lineages and fully in plants [9] where an rnpB gene (encoding RPR) has not been identified, and a functional PRORP is present in all three cell compartments (nucleus, mitochondria, and chloroplast) [7]. Reconstitution of RNase P activity from plastid RPR and bacterial RPP has been shown [16,17] It seems that plastid RPRs have lost catalytic proficiency either because they are more dependent on one or more unidentified protein subunits, or because a PRORP type enzyme has replaced its function. Red and green algae encode PRORP [8] and in the case of the prasinophyte Ostreococcus tauri, PRORP has RNase P activity in vitro [13], its cellular localization is not known. RPRs and have characterized the RPR from the chromatophore of two P. chromatophora strains to determine if in this independent, more recent evolving plastid, a similar process of RPR loss of function has happened

Results and Discussion

Experimental Section

Cloning of RPR

RNase P Assays

Conclusions