SUMOylation is critical for vimentin assembly at the ApV. (A) Knockdown of the SUMO-conjugating enzyme, Ubc9, eliminates vimentin assembly at the ApV. Untreated and HEK-293T cells treated with Ubc9, GAPDH, or non-targeting siRNA were infected with A. phagocytophilum and labeled with SUMO-2/3 and vimentin antibodies for LSCM analysis; (B) Ubc9 and GAPDH are knocked down in siRNA treated cells. Lysates of untreated and Ubc9, GAPDH, or non-targeting siRNA-treated HEK-293T cells were analyzed by Western blot with Ubc9, GAPDH, and β-actin antibodies. (A,B) KD, knockdown; (C) Keratin-8 and keratin-18 localize to the ApV in ubc9 knockdown cells. RF/6A cells treated with Ubc9 siRNA were infected with A. phagocytophilum and labeled with keratin-8 or keratin-18 antibodies for LSCM; (A,C) Asterisks (*) denote ApVs. Host nuclei and bacterial DNA were stained with DAPI (blue). Scale bars, 5 μm. Results in all panels are representative of two experiments with similar results.