Fig. 9. BOB.1/OBF.1 degradation results in downregulation of octamer-dependent transcription. (A) Ramos B cells were transfected with octamer-dependent luciferase reporter plasmids (ED contains the wild type, Ed contains a mutated octamer motif) and were incubated with anti-IgM antibodies for 20 h. (B) Downregulation of BOB.1/OBF.1 after IgM cross-linking is mediated by SIAH1. The same reporter plasmid described in (A) was cotransfected with the SIAH1 C-terminus followed by IgM cross-linking. (C) Octamer-dependent transcription is downregulated as a consequence of the BOB.1/OBF.1 degradation by SIAH1 in NIH 3T3 cells. NIH 3T3 cells were transfected with expression plasmids for BOB.1/OBF.1 and SIAH1. In addition, an octamer-dependent luciferase reporter plasmid (4× wt.TATA) was cotransfected. Eighteen hours after transfection the cells were harvested and luciferase activity measured. (D) No effect of SIAH1 was seen on the expression of thymidine kinase promoter-driven construct. Analysis as in (C).