A. Alignment of a selection of TDP1 orthologs first HxKx(n)N motif amino acid (aa) sequences. This motif provides the Hisnuc (bold) residue; the adjacent His is italicized. UniProt KB/Swiss-Prot protein #: H sapiens (Q9NUW8), S. cerevisiae (P38319), P. troglodytes (G2HG04), M. musculus (Q8BJ37), R. norvegicus (Q4G056), C. familiars (E2REL5), G. gallus (F1NSQ5), B. Taurus (F1MST1), D. melanogaster (Q9VQM4), D. rerio (E7FEK0). B. top1Δtdp1Δ yeast cells co-transformed with vector control (ytop1Δ) or -hTOPO1·U (↑hTOPO1) and the indicated YCpGAL1-hTDP1·L or its control vector (ytdp1Δ). Exponentially growing cells were corrected to an OD595 0.3 and ten-fold serially diluted, spotted onto selective galactose plates, and incubated at 30°C for 4 days.