FIG. 3.

Association of the A subunit with the B-subunit oligomer. E. coli BL21 cells were transformed with pET11 derivative plasmids carrying the holotoxin gene of LTp (pET11-5110, pET11-5130, and pET11-5120) and pET11. These transformed cells were induced with IPTG. The cells were then labeled for 1 min with [³⁵S]methionine and chased for 1 or 30 min. The periplasmic fractions of these labeled cells were prepared and incubated with αLTp-B. The resulting immunoprecipitates were gathered by centrifugation and resolved by SDS-PAGE. Radioactive bands were detected by image analysis as described in the text. The positions of the A and B subunits are indicated on the left.