(a) Jab1 decreased 9-1-1 protein degradation rate. Myc-tagged Rad1, Hus1 and Rad9 were co-transfected with empty vector or HA-Jab1 expression vector in 293T cells. After 40 hours, cycloheximide (80 μg/mL) was added to the culture, and the whole cell extracts were prepared at 0, 1, 2, 4, and 8 hours and assayed by Western blotting with an anti-Myc antibody to detect 9-1-1 expression levels. (b) The intensity of the bands in (a) was quantitated by phosphorimaging and plotted relative to the amount present at time 0. (c) Proteasome inhibitor increased Jab1-downregulated 9-1-1 protein levels. Myc-tagged Rad1, Hus1 and Rad9 were co-transfected with empty vector or HA-Jab1 expression vector in 293T cells. Cells were incubated with or without the proteasome inhibitor, MG132 (25 μmol/L), for 3 hours. Extracts were assayed by Western blotting with Myc antibody to detect Rad1, Hus1 and Rad9.