Isolation of mutants of CHO cells resistant to 6(p-hydroxyphenylazo)-uracil I. A novel BrdU cross-resistant phenotype.

Three classes of mutants resistant to the drug 6(p-hydroxyphenylazo)-uracil have been isolated from mutagenized cultures of CHO cells. One class of these mutants designated HPURA exhibits a unique form of cross-resistance to bromodeoxyuridine in that it is resistant to this drug only in the presence of thymidine. The molecular basis of the BrdU resistance is unknown but does not appear to involve the known targets of the drug. An interesting feature of these mutants is that they give rise, at a high frequency, to a subpopulation of cells which are much more resistant to BrdU.