Table 1. Genes participating in the repair of topoisomerase II mediated DNA damage^{a, b, c}.

Gene	Function	Experimental system	Reference
Artemis	Nuclease participating in some NHEJ reactions	Mutant cell line	145-147
ATM	Checkpoint signaling (Protein kinase)	Numerous	9,125,148
ATR	Checkpoint signaling (Protein kinase)	Biochemical assay, chemical inhibition	125,149,150
BRCA1	Mutated in familial breast cancer, DNA damage sensing, transcription, possible modulator of Top2 activity	Mutant cell line	71
BRCA2	Mutated in familial breast cancer, homologous recombination, DNA repair DNA damage sensing	Mutant cell line	71
CHK1	Checkpoint signaling (Protein kinase)	Biochemical assay, siRNA	150,151
CHK2	Checkpoint signaling (Protein kinase)	Biochemical assay	151,152
CtIP	BRCA1 binding protein that functions in the MEN pthway, nuclease, mammalian homolog of Sae2	Biochemical assay	64,153
DNA-PKcs	DNA dependent protein kinase catalytic subunit, required for NHEJ	Mutant cell line, siRNAd, chemical inhibition	103,146,154,155
H2AX	Histone H2A isoform, phosphorylation marks double strand breaks	Mutant cell line	156
KU70	Subunit of a DNA binding complex (with DNA-PKcs required for NHEJ	Numerous	154,157-159
KU80	Subunit of a DNA binding complex (with DNA-PKcs required for NHEJ	Numerous	154
LIG4	DNA ligase IV, a ligase specific for NHEJ	siRNA	155
MRE11	Component of the MRN complex, required for DNA damage signaling and double strand break repair	Numerous	160-162
NBS1	Component of the MRN complex, required for DNA damage signaling and double strand break repair	Biochemical assay	163,164
PLK1	Polo-like kinase	Biochemical assay	165
RAD50	Component of the MRN complex, required for DNA damage signaling and double strand break repair	Biochemical assay	166
RAD52	Homologous recombination, repair of double strand breaks by homologous recombination	Yeast	160,167,168
Rb1	Retinoblastoma susceptibility protein, control of cell cycle progression	Mutant cell line	169
TDP1	Tyrosyl DNA phosphodiesterase I	Yeaste	51,170
XPC	Nucleotide excision repair	siRNA	155,171
XPG	Nucleotide excision repair	Yeastf	51

^aTopoisomerase II targeting drugs have been frequently used in studying apoptosis. Therefore genes that affect sensitivity to Top2 targeting drugs mainly by affecting apoptosis are not included in this table.

^bSeveral genomic screens have been carried out using yeast to identify genes that confer sensitivity to Top2 targeting drugs ¹⁵⁸,¹⁷²,¹⁷³. These genes have not been discussed here unless similar genes or processes have been identified in mammalian cells.

^cThis table was assembled mainly using data using etoposide as a Top2 targeting drug. This was done to avoid the possible complication of effects of drugs (especially anthracyclines) on targets other than topoisomerase II.

^dDiscordant results have been reported for the sensitivity of DNA-PKcs deficient cells to etoposide. More recently, a DNA-Pk inhibitor has been reported to confer sensitivity to etoposide ¹⁰³.

^eTdp1 mutants have been shown to confer sensitivity to etoposide in yeast cells, but not in mammalian cells.

^fSensitivity to etoposide has been demonstrated in yeast rad2 mutants. RAD2 is the yeast homolog of XPG. Sensitivity of XPG mutants in mammalian cells has not been reported.