Schematic representation of the multiple alignment of the mRNAs of a microsomal glutathione transferase homolog gene with the genomic sequence. Three GenBank mRNAs (blue) align to the same genomic locus on chromosome 9, NT_008541 (red). Three ESTs that map to this locus are presented (purple), 38 other ESTs that align to the locus are not displayed to save space. Gaps in the alignment of mRNAs represent introns in the DNA. Four exons (marked I, II, III, and IV) are inferred from the presented alignment. Exon II is an alternative internal exon, contained entirely within an Alu repeat. Exon III is a constitutive internal exon, found in all detected splice variants and supported by seven expressed sequences (only five are shown). TheLEADS output was searched for internal exons. A total of 1176 alternatively spliced internal exons were found, 61 of them (5.2%) contained an Alu fragment. A total of 4151 constitutive internal exons were found; none of them contained anAlu fragment.