Enzyme nomenclature: Functional or structural?

Human ribonuclease P: Subunits, function, and intranuclear localization

“…Extensive purification analysis of RNase P from HeLa cells has revealed that the nuclear form of this tRNA processing holoenzyme is composed of at least 10 protein subunits associated with a single RNA species, H1 RNA (Table 1; Eder et al+, 1997;)+ These protein subunits are designated Rpp14, Rpp20, Rpp21, Rpp25, Rpp29, Rpp30, Rpp38, Rpp40, hPop5, and hPop1 (Lygerou et al+, 1996b;Eder et al+, 1997;Jarrous et al+, 1998Jarrous et al+, , 1999avan Eenennaam et al+, 1999van Eenennaam et al+, , 2001)+ The tight association of these proteins with highly purified nuclear RNase P obtained by different purification schemes implies that they constitute the core structure of the holoenzyme )+ A recent study has shown that the mitochondrial form of HeLa RNase P possesses an RNA that is identical to the H1 RNA (Puranam & Attardi, 2001)+ This enzyme has a sedimentation coefficient of ;17S in glycerol gradients, compared to ;15S of the nuclear counterpart, and exhibits properties typical of a ribonucleoprotein enzyme (Puranam & Attardi, 2001)+ This finding contradicts earlier biochemical analyses that support the concept that human mitochondrial RNase P is not a ribonucleoprotein complex (Rossmanith et al+, 1995;Rossmanith & Karwan, 1998)+ These opposing findings provoke further debate on the biochemical nature of mitochondrial and other organellar RNase P enzymes (Frank & Pace, 1998;Schon, 1999;Altman et al+, 2000;Gegenheimer, 2000;Salavati et al+, 2001), and therefore more biochemical and genetic means should be applied to resolve this issue+ Nuclear RNase P purified from Saccharomyces cerevisiae has nine distinct protein subunits and genetic studies established that these subunits are essential for yeast viability and enzyme activity in tRNA processing (see Xiao et al+, 2001)+ A multi-subunit ribonucleoprotein has also been described for nuclear RNase P purified from Aspergillus nidulans (Han et al+, 1998)+ In addition to the protein subunits described above (Table 1), several other proteins transiently interact with RNase P in yeast and human cells+ As judged by twohybrid genetic screens in yeast, the subunit Rpp20 interacts with the heat shock protein Hsp27 and the subunit Rpp14 contacts several proteins, including the LIM domain protein 1 (LIMD1) and HSPC232 ; the latter is an SR-rich protein that exhibits partial similarity to splicing factors SC-35 and SRp46+ The interaction of Rpp20 with Hsp27 was verified by biochemical analysis )+ In S. cerevisiae, a complex of seven Sm-like proteins (Lsm2-8) is associated with the precursor RNA subunit, Rpr1, of nuclear RNase ...…”

Eukaryotic Ribonuclease P: A Plurality of Ribonucleoprotein Enzymes

“…Characterization of RNase P-like activities from both mitochondria and chloroplasts have identified RNA-based enzymes similar to the nuclear and bacterial forms, as well as purely protein-based enzymes. The physiological relevance of these activities is currently under discussion (48)(49)(50).…”

Eukaryotic ribonuclease P: Increased complexity to cope with the nuclear pre-tRNA pathway

“…Spinach chloroplast RNase P has been puri®ed extensively, and has the properties of a solely protein enzyme (Wang et al, 1988;Thomas, 1996) with a pre-tRNA cleavage mechanism distinct from the RNA-based RNase Ps (Thomas et al, 2000a). Evidence concerning RNase P composition from mammalian mitochondria remains contradictory (Altman et al, 2000;Gegenheimer, 2000).…”