<i>In vitro</i>; selection for altered divalent metal specificity in the RNase P RNA | CU Experts

; The ribozyme RNase P absolutely requires divalent metal ions for catalytic function. Multiple Mg; 2+; ions contribute to the optimal catalytic efficiency of RNase P, and it is likely that the tertiary structure of the ribozyme forms a specific metal-binding pocket for these ions within the active-site. To identify base moieties that contribute to catalytic metal-binding sites, we have used; in vitro; selection to isolate variants of the; Escherichia coli; RNase P RNA with altered specificities for divalent metal. RNase P RNA variants with increased activity in Ca; 2+; were enriched over 18 generations of selection for catalysis in the presence of Ca; 2+; , which is normally disfavored relative to Mg; 2+; . Although a wide spectrum of mutations was found in the generation-18 clones, only a single point mutation was common to all clones: a cytosine-to-uracil transition at position 70 (; E. coli; numbering) of RNase P. Analysis of the C70U point mutant in a wild-type background confirmed that the identity of the base at position 70 is the sole determinant of Ca; 2+; selectivity. It is noteworthy that C70 lies within the phylogenetically well conserved J3/4-P4-J2/4 region, previously implicated in Mg; 2+; binding. Our finding that a single base change is sufficient to alter the metal preference of RNase P is further evidence that the J3/4-P4-J2/4 domain forms a portion of the ribozyme’s active site.;

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