Binding of progesterone by rat uterus in vitro

Circular dichroism (CD) spectra have been determined for chromatin fractions obtained by ECTHAM-cellulose chromatography. The molecular ellipticity at the positive long wavelength maximum is about 3000 deg cm²/dmol for early-eluted chromatin fractions, thought to be relatively repressed $\text{in vivo}$, and 5000–6000 deg cm²/dmol for late-eluted chromatin fractions, those thought to be preferentially transcribable $\text{in vivo}$. CD bands in the peptide bond spectral region also differ for the two chromatin fractions, early-eluted chromatin having a more helical conformation for proteins. In addition to previously known differences in protein content, the biological activity of a native chromatin fraction can now be correlated with the conformation of its DNA.