Several rheumatic diseases are associated with the presence of autoimmune antibodies and/or cytotoxic lymphocytes. Both systemic lupus erythematosus (SLE) and mixed connective tissue disease (MCTD) patients produce autoantibodies directed against distinct antigenic sites (Sm and RNP respectively) on the ubiquitous U1 small nuclear ribonucleoprotein particle (U1snRNP or U1RNP) of eucaryotic cells. The role that either the autoantibodies or this antigenic U1RNP plays in the development of these diseases is unknown. A reliable source of antigenic material may facilitate these inquires; preliminary data identifying anti-RNP, anti-Sm, and anti-m3G "cap" reactivity indicate that the procaryotic cyanobacterium, Synechococcus leopoliensis, may be such a source. This project proposes to characterize the Sm and RNP antigens detectable in cyanobacteria in order to determine their relationship to human cell U1RNP antigens. The trimethy1 "capped" cyanobacterial RNA will be sequenced by direct RNA and/or cDNA sequencing methodologies for correlation with known small RNA sequences. Immunoprecipitation assays and western blots of cyanobacterial extracts, using epitope-defined rheumatic disease patient autoantibodies and select monoclonal antibodies as probes, will be used to characterize further the protein and nucleic acid components of the cyanobacterial antigenic material. A competitive immunoprecipitation assay will be used to correlate the human and cyanobacterial components by determining whether cyanobacterial antigens can block the immunoprecipitation of specific human antigenic peptides and RNAs. The cellular form and intracellular distribution of the cyanobacterial reactivity will be investigated by gradient centrifugation and immunoelectron microscopic analyses. These studies they believe could contribute substantial information towards understanding the evolutionary origins of small nuclear ribonucleoprotein particles (snRNPs). Such information could elucidate the role that snRNPs play in basic cellular physiology.