Rate of translation and kinetics of processing of newly synthesized molecules of two major outer-membrane proteins, the OmpA and OmpF proteins, of Escherichia coli K12.

Abstract

The rate of synthesis of the OmpA and OmpF proteins, two of the major outer membrane proteins of Escherichia coli K12, was determined. At 25 degrees C both proteins were translated at 6.5 amino acids/s, and the OmpF protein was translated at 15 amino acids/s at 37 degrees C. The former rate corresponded to a synthesis time of just over 50 s for both proteins, which is significantly faster than their reported rates of assembly into the outer membrane at 25 degrees C. The kinetics of processing of the pro-OmpF protein were also investigated in detail, and the pro-OmpF half-life estimated to be 3-5 s at 25 degrees C. However a fraction of the precursor was processed more slowly, which may explain the discrepancy between these data and our earlier published estimate of 30 s. Pro-OmpA protein was processed with similar kinetics. These results demonstrate that the rate-limiting step in the assembly of both proteins into the outer membrane is post-translational and follows the processing step.