The TolC protein of Escherichia coli K12 is synthesised in a precursor form

Abstract
We examined the biosynthesis of the TolC protein of Escherichia coli K12 in a pulse—chase experiment, followed by immunoprecipitation with anti‐TolC antibody and SDS—PAGE of the immunoprecipitate. This showed that TolC protein was originally synthesised in a precusor form (M r 54 500) which could be chased into the mature form (M r 52 000). DNA sequencing of a portion of the cloned tolC gene showed that the N‐terminus of the mature rotein was preceded by a typical signal sequence of 22 residues (M r 2542). The initiator Met was preceded by a Shine—Dalgarno sequence, with the correct spacing.