DEFINITION OF THE TH TO RIBONUCLEOPROTEIN BY RNASE-P AND RNASE MRP/

We show that the Th/ To ribonucleoprotein is defined by (i) the co-imm unoprecipitation of two RNAs, (ii) the co-immunoprecipitation of four major polypeptides and (iii) the quantitative immune recognition of bo th RNase P and RNase MRP. No serum was found that recognizes either on e of these two enzymes exclusively. The specific co-immunoprecipitatio n of RNase MRP and RNase P by all Th/ To ribonucleoprotein autoantibod ies indicates that the anti-Th/ To autoimmune response is directed aga inst both enzymes in a quantitatively indistinguishable manner. Thus t he Th/ To ribonucleoprotein is defined by RNase P and RNase MRP.