RNase P of the Cyanophora paradoxa cyanelle: a plastid ribozyme

Biochimie. 2007 Dec;89(12):1528-38. doi: 10.1016/j.biochi.2007.08.004. Epub 2007 Aug 11.


Ribonuclease P (RNase P) is a ribonucleoprotein enzyme that generates the mature 5' ends of tRNAs. Ubiquitous across all three kingdoms of life, the composition and functional contributions of the RNA and protein components of RNase P differ between the kingdoms. RNA-alone catalytic activity has been reported throughout bacteria, but only for some archaea, and only as trace activity for eukarya. Available information for RNase P from photosynthetic organelles points to large differences to bacterial as well as to eukaryotic RNase P: for spinach chloroplasts, protein-alone activity has been discussed; for RNase P from the cyanelle of the glaucophyte Cyanophora paradoxa, a type of organelle sharing properties of both cyanobacteria and chloroplasts, the proportion of protein was found to be around 80% rather than the usual 10% in bacteria. Furthermore, the latter RNase P was previously found catalytically inactive in the absence of protein under a variety of conditions; however, the RNA could be activated by a cyanobacterial protein, but not by the bacterial RNase P protein from Escherichia coli. Here we demonstrate that, under very high enzyme concentrations, the RNase P RNA from the cyanelle of C. paradoxa displays RNA-alone activity well above the detection level. Moreover, the RNA can be complemented to a functional holoenzyme by the E. coli RNase P protein, further supporting its overall bacterial-like architecture. Mutational analysis and domain swaps revealed that this A,U-rich cyanelle RNase P RNA is globally optimized but conformationally unstable, since changes as little as a single point mutation or a base pair identity switch at positions that are not part of the universally conserved catalytic core led to a complete loss of RNA-alone activity. Likely related to this low robustness, extensive structural changes towards an E. coli-type P5-7/P15-17 subdomain as a canonical interaction site for tRNA 3'-CCA termini could not be coaxed into increased ribozyme activity.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Base Sequence
  • Cyanobacteria / enzymology*
  • Enzyme Activation
  • Escherichia coli Proteins / genetics
  • Escherichia coli Proteins / metabolism
  • Holoenzymes / genetics
  • Holoenzymes / metabolism
  • Kinetics
  • Nucleic Acid Conformation
  • Organelles / enzymology
  • Plasmids
  • Plastids / metabolism*
  • RNA Processing, Post-Transcriptional
  • RNA, Bacterial / genetics
  • RNA, Bacterial / metabolism
  • RNA, Catalytic / chemistry*
  • RNA, Catalytic / isolation & purification
  • RNA, Catalytic / metabolism*
  • RNA, Transfer / chemistry
  • RNA, Transfer / genetics
  • RNA, Transfer / metabolism
  • Recombinant Proteins / metabolism
  • Ribonuclease P / genetics
  • Ribonuclease P / metabolism*
  • Templates, Genetic
  • Transcription, Genetic


  • Escherichia coli Proteins
  • Holoenzymes
  • RNA, Bacterial
  • RNA, Catalytic
  • Recombinant Proteins
  • RNA, Transfer
  • Ribonuclease P
  • ribonuclease P, E coli