Nucleic Acids Research, 1978, Vol. 5, No. 9 3337-3346
© 1978
Articles |
Physicochemical studies on interactions between DNA and RNA polymerase. Ultraviolet absorption measurements*
Biochemistry and Molecular Biology Department, Harvard University, Cambridge, MA 02138 USA
Biochemistry Department, Stanford University School of Medicine, Stanford, CA 94305 USA
Received June 27, 1978.
The interaction between Escherichia coli RNA polymerase and a restriction fragment of coliphage T7 DNA containing four promoter sites for the coli enzyme has been studied by difference uv absorption spectroscopy in a low ionic strength buffer containing 10 mM MgCl2and 50 mM KCl. The binding of the en zyme to the DNA is accompanied by a hyperchromic shift which shows a maximum around 260 nm, and increases with increasing temperature in the temperature range studied (4–40°C). Measurements were also carried out with whole T7 DNA and a restriction fragment containing no promoter site. A comparison of the results obtained with the various DNAs suggests that the binding of an RNA polymerase to a promoter site in the low ionic strength medium causes the disruption of a short segment of the DNA helix, of the order of ten pairs; the binding of an enzyme molecule to a promoter site appears to have a cooper ative effect on the binding of enzyme molecules to adjacent non-promoter sites with concomitant disruption of DNA base pairs.
*This paper is the third of a series from this laboratory, the first two being Hsieh and Wang (1976) and Wang et al. (1977).