Figure 1.

The top1 locus at 13B6 on chromosome X, scaffold AE003498. The top locus spans 8.5 kb and encodes three different transcripts: top1-RA (5325 nt), top1-RB (2379 nt), and top1-RC (4940 nt). For simplicity, only the transcript corresponding to top1-RA is shown. The exons are represented as numbered boxes. The gray areas correspond to untranslated regions (including exon 2–7, part of exon 1, and part of exon 8), whereas the black areas correspond to protein-coding regions. Alleles of top1^G0229, top1^G0134, and top1^G0201 are P-element insertion lines. The top1¹¹² allele has a deletion in 3′ untranslated region. The P element responsible for the top1^JS mutation is inserted in the 5′ untranslated region, between nucleotides 256075 and 256076 of genomic scaffold AE003498, corresponding to 31 and 32 of the top1 mRNA variant A and C, which is 257 bp away from the translation start site.