Precursors of three exported proteins in Escherichia coli.

Abstract

Arabinose-binding protein, maltose-binding protein and [phage] .lambda. receptor are synthesized in vitro on membrane-bound polysomes from E. coli. All 3 proteins are exported from the cytoplasm of E. coli and all 3 are made in vitro in a form a few thousand daltons larger than the authentic protein. The larger form of arabinose-binding protein is also detected in vivo by pulse labeling. The larger forms of the exported proteins are precursors containing an extra sequence. In contrast to the above, when the intracellular protein elongation factor Tu is synthesized in vitro on free polysomes, it is not detectably larger than the authentic form.