FIG. 2.

Formaldehyde cross-linking indicates that CorA is a tetramer. Intact cells of E. coli DH5α, wild-type Salmonella serovar Typhimurium LT2 (MM1442), Salmonella serovar Typhimurium MM281 carrying pMAS29, a high-copy plasmid expressing CorA (MM1927), or Salmonella serovar Typhimurium MM1324, carrying the same plasmid vector expressing the Cys191Ser Cys317 CorA, were grown and treated as described in Materials and Methods. The resulting Western blot was scanned into Adobe Photoshop 5.0 and transferred into Canvas. No editing was done except some alteration of brightness and contrast. Gels from several different experiments were exposed for various times before development. Note that virtually all E. coli CorA was cross-linked by formaldehyde, while in the other three strains formaldehyde converted a large amount of monomer to higher-molecular-weight bands.