Biosynthesis and Export of Colicin A inCitrobacter freundiiCA31

Abstract

Synthesis of colicin A after induction with mitomycin C was studied. Specific inhibition of chromosomal protein synthesis occurred very shortly after mitomycin addition. There was no coordinate synthesis of colicin A (61000 M_r) and low‐molecular‐weight protein. Free and membrane‐bound polysome fractions were isolated from cells induced with mitomycin C. Colicin A is synthesized in vitro in the free polysomes and not in the membranebound polysomes. Conditions are described which allow a practically specific labelling of colicin A in vivo. By using this system it was possible to demonstrate that colicin A is not transferred cotranslationally across the cytoplasmic membrane. In contrast, this protein leaves the cell where it is made long after synthesis. Preliminary evidence. suggesting that pauses occur during synthesis of colicin A, is presented.