Figure 7.—

cin-4 is a duplication of the top-2 gene. (A) The cin-4 mRNA sequence following the SL1 spliced leader sequence. A potential upstream open reading frame is shown in the longer boxed region and the predicted cin-4 start codon is shown as boxed ATG. (B) Comparison of the structure of top-2 and cin-4 on the basis of DNA sequence alignment. A cartoon depicts the results from the alignment of the top-2 and cin-4 loci aligned using the DNA Strider Blocks alignment tool. A representation of the topoisomerase II functional domains is above the DNA alignment graphic. (C) DNA sequence alignment of intron–exon boundary sequences between top-2 and cin-4. The three intron DNA sequences (lowercase) of cin-4 are aligned with introns 1, 4, and 5 of top-2. Non-intronic DNA is shown in uppercase. (D) Amino acid sequence alignment of TOP-2 and CIN-4. Amino acid sequences were aligned using the Clustal W package of the Lasergene sequence analysis software package (DNASTAR). Amino acid identity is against a solid background. The box indicates the catalytic tyrosine present in HsTOP-2α and TOP-2 and the serine residue present in CIN-4. An asterisk indicates the glutamate 304-to-glycine change identified in mr127.