Covalent bonds and cysteine resides in MUC1 dimerization. A. Breast cancer cell line MCF-7 or HEK 293T cells transfected with MUC1-CFP were subjected to reducing ("R"; β-mercaptoethanol added) or non-reducing ("NR"; no β-mercaptoethanol) conditions, ran on separate SDS-PAGE to prevent diffusion of β-mercaptoethanol, and probed with anti-MUC1-CD. B. 293T MUC1-CFP-Fv AQA cells were treated with DSS, lysed, ran on SDS-PAGE, and probed with anti-MUC1-CD. "D" and "M" indicate expected molecular weights of dimer and monomer, respectively. Whole cell lysates (WCL) are included as controls.