Journal of Biological Chemistry
Volume 272, Issue 6, 7 February 1997, Pages 3749-3757
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Nucleic Acids, Protein Synthesis, and Molecular Genetics
Trypanosoma brucei gBP21: AN ARGININE-RICH MITOCHONDRIAL PROTEIN THAT BINDS TO GUIDE RNA WITH HIGH AFFINITY*

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RNA editing in Trypanosoma brucei is a mitochondrial RNA processing reaction that results in the insertion and deletion of uridylate residues into otherwise untranslatable mRNAs. The process is directed by guide RNAs which function to specify the edited sequence. RNA editing in vitro requires mitochondrial protein extracts and guide RNAs have been identified as part of high molecular weight ribonucleoprotein complexes. Within the complexes, the RNAs are in close contact with several mitochondrial proteins and here we describe the isolation and cloning of a gRNA-interacting polypeptide from Trypanosoma brucei The protein was named gBP21 for uide RNA-inding rotein of kDa. gBP21 shows no homology to proteins in other organisms, it is arginine-rich and binds to gRNA molecules with a dissociation constant in the nanomolar range. The protein does not discriminate for differences in the primary structures of gRNAs and thus likely binds to higher order structural features common to all gRNA molecules. gBP21 binding does not perturb the overall structure of gRNAs but the gRNA/gBP21 ribonucleoprotein complex is more stable than naked guide RNAs. Although the protein is arginine-rich, the free amino acid or an arginine-rich peptide were not able to inhibit the association to the RNAs. In contrast, the gRNA-gBP21 complex formation was sensitive to potassium and ammonium cations, thus indicating a contribution of ionic contacts to the binding.

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*

This work was supported in part by grants from the Bundesministerium für Bildung und Forschung and the Deutsche Forschungsgemeinschaft (to H. U. G.). The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The nucleotide sequence(s) reported in this paper has been submitted to the GenBank™/EMBL Data Bank with accession number(s) U61382.

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Supported by National Institutes of Health Grant GM42188.

1

    The abbreviations used are:

    gRNA

    guide RNA

    RNP

    ribonucleoprotein

    PCR

    polymerase chain reaction

    nt

    nucleotide.