Detection of conformational and net charge differences in DNA‐protein complexes by quantitative electrophoresis on polyacrylamitie‐agarose copolymer gels

Abstract

The Galactosidase repressor (GalR) of Escherichia coli modulates the expression of the gal operon by binding to two DNA operators, OE and O1. The OE and O1 elements are 16 bp pallindromic DNA sequences, differing in four of the base pairs. OE and O1 DNA fragments, both free and complexed with repressor, were analyzed by "quantitative gel electrophoresis". By the criteria of that method, applied to the linear Ferguson plots of both DNA fragments and the linear ranges of those of the DNA-GalR complexes, it was shown that the apparent size of DNA increases upon repressor binding. Moreover, this size increase is greater for the complex with the O1 operator than for the complex with the OE operator in the case that GalR is located in the center of a 155 bp DNA fragment. This is not the case when GalR is located in a peripheral position. By contrast with their size differences, the centrally located GalR-O1 and GalR-OE complexes appear to possess indistinguishable net surface charge densities as judged from the intercepts with the mobility axis. The larger size of the complex with centrally located O1 fragment, as compared with that bearing the OE fragment, is interpreted as being due to bending of the DNA-protein complex, since an authentically bent fragment of a plasmid with bent upstream activator sequence also exhibits a larger slope of the Ferguson plot, and thus the larger size, than predicted on the basis of its DNA chain length (bp).(ABSTRACT TRUNCATED AT 250 WORDS)

On-Line Concentration and Separation of Proteins by Capillary Electrophoresis Using Polymer Solutions

“…In addition, the reduction in EOF was much greater than the reduction in EPM of CA when PEO solutions were changed from 0.5 to 1.0% (results not shown). This is much higher than our prediction based on the known effects of viscosity changes and retardation. , , Thus, PEO adsorption also played major roles in reducing the EOF. The fact that EOF coefficients obtained at pH 9.0 were higher than that at pH 10.0 was likely due to less PEO adsorption because of a larger amount of borate.…”