Studies on the gene for the multivalent vitamin B sub(12) receptor of Escherichia coli

The Escherichia coli btuB cistron was identified in a lambda L47 gene bank constructed using chromosomal DNA from strain W3110. The product encoded by a multicopy recombinant plasmid was observed in the outer membrane, its presence leading to reduction in the amounts of 3 major outer membrane proteins. Analysis of the plasmid-borne gene indicated that removal of the carboxy-terminal region affected receptor function, without apparently preventing export to the outer membrane. Vitamin B sub(12)-dependent regulation of btuB expression was demonstrated, despite the gene being on a high copy number plasmid.