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A G-to-A substitution at the first nucleotide at the 5' boundary of intron 10 following the transmembrane exon 10 results in two different aberrantly spliced transcripts putatively expressed in a tissue specific manner. A deletion of 107 bp was found in transcripts from mast cells of mutant mice. A deletion of 234 bp was found in transcripts from brain or bone marrow cells. The mutation disrupts splice donotr site G-GT by changing it to G-AT point, thereby causing exon skipping. The 107 bp deletion could have resulted from skipping of a transmembrane region exon and the 234 bp deletion from skipping 3 exons. The 107 bp deletion would create a frame shift with a stop codon 12 bp downstream, whereas the larger deletion would still be in frame. Northern blot analysis indicated that mast cells from mutants have only 31-37% of the transcripts as mast cells derived from normal bone marrow, suggesting that the mutation may reduce efficiency and authenticity of transcription and splicing. (J:91867)