FIG. 5.

Strep-tag pull down assay of coexpressed Strep-tag II-CT671 and His₆-CT670. (A) Coomassie blue-stained 12% SDS-PAGE gel of Strep-tagged CT671 elution fractions from Strep-tactin chromatography. CT671 eluted at 34 kDa. (B) Elution fractions from the assay were transferred to a nitrocellulose membrane and exposed to anti-CT670 antibodies for Western blot analysis as described in Materials and Methods. Antibodies recognized CT670 at 23 kDa in the elution fractions, indicating that it copurified with Strep-tagged CT671. In control experiments with cells expressing only His₆-CT670, no binding to the Strep-tactin column was observed (not shown). (C) Cell extract (CE) from E. coil BL21 cells expressing CT670 or with no expression plasmid (control) was exposed to anti-CT670 antibodies. Antibodies recognized only the overexpressed CT670 protein.