The nuclear autoantigen La/SS-B: mapping and sequencing of the gene and the three retropseudogenes

One target of autoantibodies in sera of patients with systemic lupus erythematosus or primary Sjögren's syndrome is the nuclear autoantigen La/SS-B. Lambda clones and cosmids were isolated, which contained the sequences of the La gene and the three La pseudogenes. They were used for preparation of a physical map. Finally, the La gene and pseudogenes were sequenced. The pseudogenes were characterized as retropseudogenes. Their evolutionary ages were estimated to be approx. 4, 4.5 and 5 million years. Inserts of 4, 16 and 24 nucleotides, which were mostly A-residues, were found in exon 7 of the respective pseudogene. The oldest pseudogene contained the longest insert, the youngest pseudogene contained the smallest insert. The oligonucleotides seem to be the result of repeated inserts of A-residues in a hot spot region of the La genes. Two La cDNAs were isolated which contained either a deletion or an insert of an A-residue at the same position.