the mutant frequency at five genetic loci ( resistance to ouabain , 6-thioguanine , excess thymidine , methotrexate and 1-beta-d-arabinofuranosyl cytosine ) was assayed in wild-type cells and trifluorothymidine in tk+/- cells .
C0040077
thymidine
C0040987
trifluorothymidine