THE 2 ISOFORMS OF THE 90-KILODALTON NUCLEOLUS ORGANIZER REGION AUTOANTIGEN (UPSTREAM BINDING-FACTOR) BIND WITH DIFFERENT AVIDITY TO DNA MODIFIED BY THE ANTITUMOR DRUG CISPLATIN

It has been previously described that some proteins containing HMG box es are able to bind more strongly to DNA modified with cis-diamminedic hloroplatinum(II) (cisplatin) than to unmodified DNA. In the present s tudy, we analyzed the interaction of cisplatin-modified DNA with the h uman autoantigen NOR-90 (UBF), a transcription factor that contains se veral HMG boxes. Using autoantibodies against NOR-90 to perform ELISA and immunoprecipitation, it was confirmed that NOR-90 (UBF) was able t o bind cisplatin-modified DNA more avidly than unmodified DNA or trans -diamminedichloroplatinum(II) (transplatin) modified DNA. Moreover, by Southwestern, we observed that the 97 kDalton isoform of NOR-90 (UBF1 ) was able to bind cisplatin-modified DNA more strongly than the 94 kD alton isoform (UBF2); binding of unmodified DNA or transplatin-modifie d DNA was not detected with either isoform. Sera containing autoantibo dies against NOR-90 did not inhibit, but increased the binding of NOR- 90 to cisplatin-modified DNA.