The effects of pH on the torsional flexibility of DNA bound to a
nucleosome core particle were investigated by studying the time-resolved
fluorescence anisotropy decays of ethidium bromide intercalated into the DNA
of the core particle. As the torsional flexibility of DNA is affected by the
presence of an intercalating dye, the decays were studied at different ethidium
bromide to core particle binding ratios. The anisotropy decays were collected
using the method of time-resolved single-photon counting and were fit to a
model developed by J. M. Schurr (Schurr, 1984) using a non-linear least
squares fitting algorithm developed by the author for this purpose. It was
shown that below a binding ratio of 0.1 there was no demonstrable change in
the anisotropy as a function of binding ratio. Our results show, that the
apparent torsional flexibility of DNA of to a nucleosome core particle is
dependent on the number of base pairs of the DNA between points of
attachment to the histone core. If this number is as high as 30 base pairs, then
the torsional flexibility of DNA on a nucleosome core particle is as high or
higher than DNA free in solution. Also, for reasonable values of N, the friction
felt by the DNA on a core particle is much higher than that felt by free DNA.
This indicates that the DNA on a core particle is highly constrained in its
motions. The hydrogen ion concentration was shown to have a substantial
effect on the fluorescent anisotropy decays, particularly in the early regions of
the decay. These analyses indicated that the observed change could be
attributed to either a loosening of the contacts between the DNA and the
histone core, or a relaxing of the torsional flexibility of the DNA. / Graduation date: 1991
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/37666 |
| Date | 20 July 1990 |
| Creators | Winzeler, Elizabeth A. |
| Contributors | Small, Enoch W. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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