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Volume 271, Number 28, Issue of July 12, 1996 pp. 16559-16566
©1996 by The American Society for Biochemistry and Molecular Biology, Inc.

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Ribonuclease P of Tetrahymena thermophila

(Received for publication, January 18, 1996, and in revised form, April 3, 1996)

Heather L. True and Daniel W. Celander ^§

From the  Department of Microbiology and ^§ College of Medicine, University of Illinois, Urbana, Illinois 61801

Ribonuclease P (RNase P) is responsible for the generation of mature 5 termini of tRNA. The RNA component of this complex encodes the enzymatic activity in bacteria and is itself catalytically active under appropriate conditions in vitro. The role of the subunits in eucaryotes has not yet been established. We have partially purified RNase P activity from the ciliate protozoan Tetrahymena thermophila to learn more about the biochemical characteristics of RNase P from a lower eucaryote. The Tetrahymena RNase P displays a pH optimum and temperature optimum characteristic of RNase P enzymes isolated from other organisms. The K_m of the T. thermophila enzyme for pre-tRNA^Gln is 1.6 × 10⁷ M, which is comparable to the values reported for other examples of RNase P. The Tetrahymena RNase P is a ribonucleoprotein complex, as supported by its sensitivity to micrococcal nuclease and proteinase K. The buoyant density of the enzyme in Cs₂SO₄ is 1.42 g/ml, which suggests that the RNA component of the Tetrahymena enzyme comprises a significantly greater percentage of the holoenzyme than that determined for RNase P of other Eucarya or Archaea. The holoenzyme has a requirement for divalent cations displaying characteristics that are unique for RNase P but closely resemble preferences reported for the Tetrahymena group I intron RNA. Puromycin inhibits pre-tRNA processing by the Tetrahymena complex, and implications of the similarities between recognition of tRNA by ribosomal components and RNase P are discussed.

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