CHARACTERIZATION OF RIBONUCLEASE-P FROM TOXOPLASMA-GONDII

Toxoplasma gondii ribonuclease P (RNase P) activity was identified and characterized. The enzyme cleaved the precursor of Escherichia coli t yrosine transfer RNA at a position identical to the site recognized by E. coli RNase P. The enzyme has a broad pH optimum from 7 to 9, is mo re active at 42 degrees C than at 32 degrees C and 37 degrees C, and i s relatively stable at 37 degrees C and 42 degrees C, but not at 56 de grees C. Its activity is stimulated significantly as the concentration of Mg+2 is increased to 100 mM, but some activity remains in the pres ence of less than 1 mu M free Mg+2; Ca+2 stimulates activity modestly up to 25 mM. Toxoplasma gondii RNase P differs from host (murine perit oneal exudate cells) RNase P, as indicated by its elution from cationi c ion exchange columns at a relatively high salt concentration. It is effectively inhibited by mature tRNA and inactivated by pretreatment w ith micrococcal nuclease, thus indicating the presence of an essential RNA component. Correspondingly, a number of RNA molecules, ranging in size from about 170 to 490 nucleotides, are found in T. gondii RNase P containing fractions. This study provides the basis for further char acterization of the structure and function of T. gondii RNase P and it extends the range of organisms in which RNase P has been characterize d.