Characterization of alternatively spliced PIG-A transcripts in normal and paroxysmal nocturnal hemoglobinuria cells

The genetic lesion in paroxysmal nocturnal hemoglobinuria (PNH) cells resides in a DNA element that 1) encodes a product required for assembly of GlcNAc-inositol phospholipid and 2) is commonly affected in different patients. In this study, three alternative mRNA transcripts (1600, 1200, and 950 bp) that derive from this genetic element in normal cells were characterized. The 1200-bp transcript was found to arise from splicing out of 374 bp of exonic sequence extending from positions 407-780. The 950-bp transcript was found to arise from removal of this and 284 bp of additional exonic sequence beginning further upstream at position 123. Analyses of transcripts expressed in Epstein-Barr virus (EBV)-transformed B lymphocytes prepared from two PNH patients showed that both failed to express normal 1600-bp transcripts. One expressed truncated transcripts of 1000 and 800 bp generated by an alternate splice which utilized a downstream signal in place of the normal intronic splice signal. The other expressed a 1600-bp transcript with multiple nucleotide changes but normal 1200- and 950-bp "spliced" transcripts.