Biosynthesis of Escherichia coli Braun's lipoprotein precursors in vitro and binding to membrane vesicles.

A cell-free system only programmed by endogenous mRNA present in a 30000 X g supernatant fraction is described in which 15-40% of the material produced was constituted by two lipoprotein precursors. These two polypeptides (a) are immunologically related, (b) contain the signal peptide and (c) apparently differ by the presence in one of them of a substituent on the -SH group of the single cysteine residue. The nature of this substituent could not be determined but no evidence was obtained that it could be a glyceride. No processing of any of these prolipoprotein forms could be demonstrated by addition of either Triton X-100 or membrane vesicles. A similar binding of both precursors to inverted membrane vesicles was observed when they were provided either co-translationally or post-translationally and this reaction occurred without the help of major membrane compounds.