Macromolecular crowding increases binding of DNA polymerase to DNA: an adaptive effect.

Macromolecular crowding extends the range of ionic conditions supporting high DNA polymerase reaction rates. Reactions tested were nick-translation and gap-filling by DNA polymerase I of Escherichia coli, nuclease and polymerase activities of the large fragment of that polymerase, and polymerization by the T4 DNA polymerase. For all of these reactions, high concentrations of nonspecific polymers increased enzymatic activity under otherwise inhibitory conditions resulting from relatively high ionic strength. The primary mechanism of the polymer effect seems to be to increase the binding of polymerase to DNA. We suggest that this effect on protein-DNA complexes is only one example of a general "metabolic buffering" action of crowded solutions on a variety of macromolecular interactions.