| We observe that degradation of trapped TOP 2 cleavable complexes , liberation of DNA strand breaks , and repair of those breaks occurs more efficiently in cells expressing Rb 1 protein ( pRb ) . ^^^ Rb 1 mediated processing and repair of TOP 2 cleavable complexes is genetically separable from its ability to bind E2F and enforce DNA damage induced cell cycle checkpoints . ^^^ Rb 1 protein binds both TOP 2 and BRCA 1 in intact cells , and pRb is required for association between TOP 2 and BRCA 1 . ^^^ |