ALTERNATIVELY SPLICED EXONS ENCODE THE TISSUE-SPECIFIC 5'-TERMINI OF LEUKOCYTE PP52 AND STROMAL CELL S37 MESSENGER-RNA ISOFORMS

The pp52 gene encodes an intracellular, F-actin-binding phosphoprotein (also designated LSP1 and WP34) postulated to function in cytoskeleto n dynamics and cell motility. We previously reported that different mR NA isoforms are expressed from this gene in cells of the leukocyte lin eage versus mesodermally derived cells. These tissue-specific mRNA iso forms are identical except for 5'-untranslated regions and sequences c oding for unique N-termini of 23 and 21 amino acids, respectively. As this is a single-copy gene, we predicted that these tissue-specific mR NA isoforms would be generated by alternative RNA splicing. We report that the unique 5' sequences in these mRNA isoforms are encoded in two separate exons containing ATG initiation codons. These features confi rm that the pp52 and S37 mRNA isoforms are generated by alternative RN A splicing and establish that they are independently translated. Other results presented here indicate that the differential expression of t hese exons in leukocytes versus mesodermally derived cells is regulate d at the level of transcription by tissue-specific promoters. (C) 1996 Academic Press,Inc.