Hepatitis B surface antigen assembles in a post-ER, pre-Golgi compartment

The stably transfected mouse L fibroblast cell line SV24, expressing the short form (S) of hepatitis B surface antigen, subtype adw, under the control of the SV-40 early promoter (Simon et al., 1988) , was a kind gift from Dr. Don Ganem (University of California, San Francisco, CA). The cells were grown in DME containing 2.2 g/liter sodium bicarbonate, 10% (vol/vol) FCS, 10 mM Hepes, 2 mM glutamine, 100 U/rni penicillin, and 100 t~g/ml streptomycin, in a standard cell incubator at 37~ in 5% CO2 atmosphere. Rat PDI-cDNA was obtained from Dr. George Banting (Bristol University, UK). Pansorbin and polyclonal rabbit antiserum against human HBsAg were purchased from Calbiochem-Behring Corp. (La lolla, CA). Attinitypurified rabbit antibody against the COOl-t-terminus of rab2 (Chavrier et al., 1990) was kindly provided by Dr. Marino Zerial (EMBL, Heidelberg, Germany). Sheep antibody against human HBsAg (#61WG20, Behringwerke, Marburg, Germany) was a generous gift from Dr. Michael Nassal (Zentrum ftir Molekularbiologie, Heidelberg, Germany) and it was used with permission from Behringwerke. Rhodamine-conjugated goat-antirabbit-IgG antibodies were from Jackson Immunoresearch Laboratories Inc. (West Grove, PA) and from Southern Biotechnology Associates (Birmingham, AL). Flnorescein-conjugated goat antibodies against mouse IgG (gamma chain specific) were from Zymed (San Francisco, CA). Hoechst 33258 DNA stain was from Hoechst (Frankfurt a/M, Germany). Alkaline phosphatase-conjugated goat-anti-rabbit-IgG (whole molecule) and goatanti-mouse-IgG (gamma chain specific) were purchased from Zymed.