The effect of translation and transcription inhibitors on the synthesis of periplasmic phosphatases in E. coli

Biosynthesis and export of colicin A in Citrobacter freundii CA31

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 Mr) 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 membrane-bound 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 was made long after synthesis. Preliminary evidence, suggesting that pauses occur during synthesis of colicin A, is presented.

ExpA: a conditional mutation affecting the expression of a group of exported proteins in Escherichia coli K-12

A mutant of Escherichia coli K-12 was isolated as conditionally deficient in the expression of two exported proteins simultaneously (i.e. two acid phosphatases). The mutant was found to be thermosensitive on minimal medium at 37 degrees C and above, but grew normally on rich media at these temperatures. The mutation, named expA and located at 22 min on the recalibrated linkage map, depressed the levels of six periplasmic enzymatic activities in bacteria grown at 37 degrees C. At least ten proteins were greatly reduced in the periplasm under these conditions. The mutation also affected some outer membrane proteins, among which were the ompF protein and a protein which may be protein III, but had little effect on cytoplasmic membrane proteins. The gel patterns of the soluble cytoplasmic proteins were not modified except for one major protein of MW 47,000. The activities of beta-galactosidase and of aspartate transcarbamylase were unmodified. After growth at 30 degrees C no difference was observed between expA and expA+ isogenic strains. The results are discussed with respect to the mechanism of protein export.

Modulation of an apparent mRNA pool for extracellular protease in Bacillus amyloliquefaciens

Late-log-phase cells of Bacillus amyloliquefaciens have the unusual capacity to produce extracellular protease for over 60 min in the presence of rifampin or actinomycin D at levels which strongly inhibit incorporation of amino acids into cellular protein. If cells are incubated in the presence of high levels of amino acids for 75 min this capacity is exhausted, but it is retained if the incubation is carried out in low levels of amino acids. Transfer of exhausted cells from high to low concentrations of amino acids results in a progressive recovery of the capacity for rifampin-actinomycin-insensitive protease production. The results seem best explained on the basis of the accumulation of a reserve pool of mRNA for extracellular protease. Measurement of the apparent mRNA pool size over 12 h shows a cyclical rise and fall, and these changes correlate with a periodic variation of the rate of protease production. A working hypothesis is presented to account for these observations in terms of a novel control situation over protease mRNA transcription.