CHARACTERIZATION OF 2 SCLERODERMA AUTOIMMUNE ANTIGENS THAT COPURIFY WITH HUMAN RIBONUCLEASE-P

Human RNase P has been purified more than 2000-fold from HeLa cells, I n addition to the RNA component, H1 RNA, polypeptides of molecular mas ses 14, 20, 25, 30, 38, and 40 kDa copurify with the enzyme activity, Sera from two different patients with the autoimmune disease scleroder ma were used to immunodeplete human RNase P activity. These same sera cross-reacted on immunoblots with two of the copurifying polypeptides, p30 and p38, whereas an autoimmune serum that does not immunodeplete RNase P activity did not react with these proteins, Peptide fragments derived from purified p30 and p38 facilitated the molecular cloning an d sequencing of cDNAs coding for these two polypeptides, which are now designated as Rpp30 and Rpp38, respectively, RPP38 cDNA encodes a pol ypeptide that may be identical to a previously identified antigen of a pproximate to 40 kDa, which is immunoprecipitated by Th and To autoimm une antisera, and that has been implicated as a protein subunit of hum an RNase P by virtue of its ability to bind to H1 RNA in vitro. The se cond autoimmune antigen, Rpp30, as such, has not been described previo usly.