CLONING AND EXPRESSION OF MOUSE 60 KDA RIBONUCLEOPROTEIN SS-A RO/

Autoantibodies to SS-A/Ro are among the most common found in sera of p atients with systemic rheumatic diseases. These autoimmune diseases ca n affect various organ systems of the body and are variable in their m anifestations and presentation. One of the autoimmune targets is the 6 0 kDa SS-A/Ro protein known to be associated with small cytoplasmic Y RNAs. To study systematically the expression of the protein, we have c loned the mouse full length 60 kDa SS-A/Ro cDNA using 5' RACE based on a cDNA sequence reported in the mouse genome project. The recombinant protein derived from the putative full-length construct was shown to react with human prototype anti-SS-A/Ro serum Ge in western blot and i mmunoprecipitation and comigrated with cellular 60 kDa SS-A/Ro protein in 3T3 cells. Cellular expression, measured by RT-PCR, was highest in mouse brain, followed by lung, muscle, kidney and heart. Lower levels were found in testis, liver and spleen. Like the human 60 kDa SS-A/Ro protein, the deduced mouse homolog has 538 amino acids. Sequence anal ysis showed 89.9% identity and 95.0% similarity between the mouse and human proteins.