Varieties of RNase P: A nomenclature problem?

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Abstract
Twenty-five years ago, a basic tenet of biochemistry held that enzymes are made solely of protein. Ribosomes, which are large ribonucleoprotein enzymes, were conveniently overlooked (but see Woese, 1967; Crick, 1968; Orgel, 1968). The then current orthodoxy was first challenged by the discovery that Escherichia coli RNase P had an essential RNA subunit (Stark et al., 1978) and completely demolished when the catalytic properties of RNA were described (Kruger et al., 1982; Guerrier-Takada et al., 1983; Buzayan et al., 1986; Hutchins et al., 1986). With respect to RNase P, in particular, a new orthodoxy arose: RNase P from any source would have an essential RNA subunit although not necessarily a catalytic one. This adolescent orthodoxy is now being challenged by reports of putative RNase P activities isolated from certain organelles that lack an RNA subunit (Manam & van Tuyle, 1987; Rossmanith & Karwan, 1998; Wang et al., 1998). The following questions must be asked of the aforementioned data: (1) Are the substrate specificities the same as in the canonical reaction? (2) Are the chemical mechanisms of the newly identified “RNase P” reactions identical to the canonical reaction? (3) Have completely purified (i.e., cloned, expressed, and/or purified) activities been studied? (4) Have the phenotypes of these “new” enzymes been verified by genetic means? (5) In sum, are we dealing with RNase P or some other activities that share some characteristics with RNase P? Should these be called RNase P, in any case?