title: Precursor proteins are intermediates in vivo in the synthesis of two major outer membrane proteins, the OmpA and OmpF proteins, of Escherichia coli K12.
abstract: The OmpA and OmpF proteins are major outer membrane proteins of Escherichia coli K12. Their precursors, the pro-OmpA and pro-OmpF proteins, have been detected in vivo in pulse-labelling experiments carried out with [35S]methionine at 25 degrees C. Wehn the pulse was at 37 degrees C, however, no precursors were detected. The pulse-labelled precursors were processed rapidly and quantitatively into mature protein at 25 degrees C. The apparent half-life of the pro-OmpF protein was estimated to be 30 s, and the pro-OmpA protein may be processed even faster. In short pulses (10 s) the precursors of both proteins were the predominant labelled species, indicating that at 25 degrees C processing does not start until chain elongation of the precursor is almost, if not entirely, complete. When French press lysates of cells pulse-labelled for 10 s were subjected to sucrose gradient centrifugation to separate the inner and outer membranes, both precursors comigrated with the inner membrane.
mesh_terms: D002499:Centrifugation, Density Gradient; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000378:metabolism*; D008565:Membrane Proteins / Q000096:biosynthesis*; D011233:Precipitin Tests; D011498:Protein Precursors / Q000302:isolation & purification*
chemical_list: D008565:Membrane Proteins; D011498:Protein Precursors