The circular dichroism properties of phi W-14 DNA containing XXXX .

@entity1472 @entity7224 @entity1391 @entity17258 @entity4113 @entity526 @entity72311
The circular dichroism properties of phi W-14 DNA containing @entity72311 and its acetylated derivative have been examined in a number of aqueous solvents. Native phi W-14 DNA exhibits a B-type CD spectrum whose characteristics do not entirely conform to what would be expected for its GC content (51%). The conformationally sensitive positive band above 260 nm has a rotational strength greater than that normally found in prokaryotic DNAs of comparable GC content, such as @entity526 DNA. The rotational strength of this band in the spectrum of the heat-denatured form of phi W-14 DNA, however, is similar to that of heat denatured @entity526 DNA. Abolition of the positive charge on the @entity7224 residues of native phi W-14 DNA by reaction with @entity17258 or by acetylation reduces the rotational strength to a level appropriate for its GC content. Increases in the electrolyte content of the solvent have the same effect, although the rotational strength of this band in phi W-14 DNA does not become comparable to that of @entity526 DNA until 6-7 M @entity4113 . Titration to pH 10.6 in solvents of modest electrolyte content, however, fails to appreciably affect the CD spectral properties of either native phi W-14 DNA or the derivative in which half of the secondary and all of the primary @entity1472 groups have been acetylated. On the basis of these results we have concluded that the enhanced rotational strength of the positive band above 260 nm in the CD spectrum of phi W-14 DNA is due to a conformational difference caused by an ion-pair interaction of the positively charged primary @entity1472 groups of @entity7224 with the @entity1391 backbone. The CD spectral properties, however, reveal that these differences, averaged over the entire basepair population, appear to be relatively small. The average conformation, at least in dilute aqueous solutions, seems to be an unexceptional B variant with conformational properties which would be more appropriate for a DNA of higher CG content.
