Figure 10. top2 hypomorphic mutants confer resistance to LS1 and other Top2 poisons. LS1 resistant top2 mutants were selected as described in Methods and Methods using the host JN394 top2ts2-4 rad52∆ strain in combination with hydroxylamine mutagenesis of the YCpDED1-TOP2 plasmid that complements the chromosomal top2ts2-4 allele. (A) LS1 sensitivity of four representative LS1 resistant top2 alleles. Growth rates were determined using the BioScreen C system and fit using the BGFit web-server as described in Materials and Methods. LS1 resistant top2 alleles also confer resistance to other Top2 poisons. (B) Cell extracts from strains LS1 resistant top2 alleles exhibit reduced Top2 activity using the kDNA assay. (C) top2-28 cells exhibit increased resistance to multiple Top2 poisons, including LS1, ellipticine (ELLIP), etoposide (ETOP) and doxorubicin (DOX). All poisons were used at a concentration of 50µM and growth rates were compared to control (0.1% DMSO) and determined as in panel (A).