BIOPHYSICAL COMPENSATION MECHANISMS BUFFERING ESCHERICHIA-COLI PROTEIN-NUCLEIC ACID INTERACTIONS AGAINST CHANGING ENVIRONMENTS

Escherichia coil adapts to changes in growth osmolarity of at least 10 0-fold by making large changes in the amounts of intracellular water a nd solutes, including cytoplasmic K+. A wide range of in vitro salt, s olute and biopolymer concentrations should therefore be considered 'ph ysiological'. Paradoxically, these large, osmotically induced changes in cytoplasmic K+ concentration do not greatly affect the equilibria a nd kinetics of cytoplasmic protein-nucleic acid interactions. Biophysi cal effects resulting from changes in the amount of cytoplasmic water (such as macromolecular crowding) and in the concentrations of other c ytoplasmic solutes appear to compensate for the effects of changes in cytoplasmic K+ concentration and thereby maintain protein-nucleic acid equilibria and kinetics in the range required for in vivo function.