UoC-M1 does not monoubiquitinylate FANCD2. A lymphoblastoid cell line control from an FA-C patient (HSC536N) does not exhibit the monoubiquitinylated form of FANCD2 (FANCD2-L), whereas retroviral correction of the FANCC defect in these cells (HSC536N/FANCC) restores FANCD2-L. UoC-M1 is incapable of forming FANCD2-L. The 4081 lymphoblastoid cell line (from the same patient as the UoC-M1 myeloid cell line) demonstrates FANCD2-L that is capable of being immunodepleted with a monoclonal antiubiquitin antibody (lane 1; ub. dep. 4081). Both Mo7e (a factor-dependent myeloid leukemia cell line) and JY (an EBV-transformed lymphoblastoid line from a healthy volunteer) demonstrate cellular resistance to MMC and FANCD2-L.