Appearance of Elongation Factor Tu in the Outer Mernbrane of Sucrose‐Dependent Spectinomycin‐Resistant Mutants ofEscherichia coli

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Abstract
When sucrose-dependent spectinomycin-resistant (Sucd-Spcr) mutants of E. coli were grown in the absence of sucrose, a new protein appeared in the membrane fraction insoluble in Triton X-100. The protein had a hydrophobic nature. Unlike other outer membrane proteins the new protein was extracted with sodium dodecyl sarcosinate. The new protein was found to be identical with elongation factor Tu (EF-Tu), as judged from the electrophoretic mobility in 3 different gel systems, coprecipitation with the antiserum against EF-Tu, the profiles of peptide fragments produced with 3 different proteases and analyses of N-terminal and C-terminal amino acids. This membrane EF-Tu accounted for 5-10% of total cell EF-Tu. When spheroplasts were pretreated with trypsin, EF-Tu in the outer membrane disappeared. Incubation of cytosol EF-Tu with the outer membrane did not result in the binding of EF-Tu to the membrane. The appearance of EF-Tu in the outer membrane is apparently not due to artificial binding during membrane preparation. The ribosomal alteration may have resulted in dislocation of the cytosol protein into the outer membrane.