THE NUCLEAR AUTOANTIGEN LA SS-ASSOCIATED ANTIGEN-B - ONE GENE, 3 FUNCTIONAL MESSENGER-RNAS/

Transcription of the gene encoding for the nuclear autoantigen La resu lted in three mRNA forms. A promoter switching combined with an altern ative splicing pathway replaced exon 1 with either exon 1' or exon 1 ' '. The exon 1 '' donor splice site was located 4 nts downstream of the exon 1' donor splice site. All three La mRNA forms were expressed in all the tissues analysed including peripheral blood lymphocytes, liver , fetal spleen, cultured primary endothelial cells, and mouse LTA cell lines permanently transfected with the human La gene. Both the exons 1' and 1 '' had unusual structures. They contained GC-rich regions and an oligo(U)-tail of 23 uridine residues. Moreover, they encoded for t hree open reading frames upstream of the La protein reading frame. In spite of this unusual structure, when exon 1' or exon 1 '' La mRNAs we re expressed in transfected mouse LTA cells, both La mRNAs were transl ated to nuclear La protein, indicating that all La mRNA forms are func tional mRNAs.