Strain and temperature-dependent variation in the amount of BtuB polypeptide in the Escherichia coli K-12 outer membrane

Abstract The outer membrane protein BtuB of Escherichia coli K-12 is the receptor for vitamin B₁₂; it is normally present in approx. 200 copies per cell. We describe here the conditions by which BtuB was readily observed in electropherograms of outer membrane preparations. These conditions are as follows. (1) Incorporation of 8 M urea in sodium dodecyl sulfate-polyacrylamide gel systems improved detection of the polypeptide. (2) In most E. coli K-12 strains examined, BtuB was most abundant when cells were grown at 27°C. This thermoregulation of BtuB was independent of envZ and envY , two regulatory genes for outer membrane proteins.