EFFECTS OF MOLECULAR CROWDING ON THE INTERACTION BETWEEN DNA AND THE ESCHERICHIA-COLI REGULATORY PROTEIN TYRR

Fluorescence quenching has been used to measure quantitatively the eff ects of sucrose and triethylene glycol on the interaction between the Escherichia coli regulatory protein TyrR and a 30-basepair oligonucleo tide containing the strong TyrR box of the TyrR operon. It was observe d that the apparent binding constant increased in the presence of co-s olutes, the dependence of the logarithm of the apparent binding consta nt on molar concentration being indistinguishable and essentially line ar for both cc-solutes. This activation of the TyrR-oligonucleotide in teraction is attributed to thermodynamic nonideatity arising from mole cular crowding, an interpretation which is supported by the reasonable agreement observed between the experimental extent of reaction enhanc ement and that predicted on the statistical-mechanical basis of exclud ed volume.