FIG. 1.

The Drosophila Ada2b locus. (A) The dAda2b locus is drawn to scale. It spans 3.4 kb and contains four exons (open boxes). The alternative splicing that occurs in exon 3 is indicated, together with the stop codons in exon 4 that terminate the alternative reading frames. Stippled boxes indicate the last exons of the flanking genes CG9636 and DNA pol iota. The location of the P-element EP(3)3412 is indicated by a triangle. Two of the deletions generated by imprecise excision of this P element are shown. The gray box indicates the genomic sequence present in the transgene that rescues the dAda2b alleles. (B) Comparison of the two protein isoforms generated by alternative splicing. Isoform a is present in the EST clone LD 24527 and is the same protein sequence as described in reference 36. The b isoform was described in reference 28. The conserved ZZ and SANT domains are boxed, and Ada boxes 1 to 3 are shaded gray. (C) RT-PCR results with RNA prepared from wild-type (wt) or dAda2b¹ or dAda2b² homozygous mutant pupae are shown at the left. The upper panel shows 930- and 1,008-bp products generated with an Ada2b primer pair, and the lower panel shows the RP49 product (control). With a different primer pair, the alternative splice site usage in dAda2b exon 3 is evident (upper right panel). Isoform a generates a 262-bp product, whereas isoform b gives rise to a 184-bp product.