Nucleoproteins nucleohistones

Fig. 12.6. Infrared absorption spectrum of partial nucleoprotein which was obtained by exposing calf thymus nucleohistone to 1.2M NaCI.

Bradbury et al. (1967) have studied partial nucleoproteins produced by removal of histone fractions from nucleohistone. Figure 12.6 shows a polarized infrared spectrum of one of the nucleoproteins oriented by shearing. The spectrum is that of a film deuterated by D2O vapor. The bands of the in-plane vibrations of cytosine and guanine moieties are highly polarized when the electric vector is placed perpendicular to the fiber axis. The 1452 cm absorption is that of the amide IF band (Miyazawa et al., 1956 Miyazawa, 1962) for the readily deuterated fraction of the partial nucleoprotein. As seen in Fig. 12.6, the 1452 cm band is polarized considerably in the direction parallel to the fiber axis, giving evidence that the extended polypeptide chain is situated so that its axis lies between the angle of the groove in the DNA double helix and the axis of the DNA helices (Bradbury et al., 1967). 

The configurational relationship between histones and DNA remains ambiguous, mainly because no clear-cut results can be obtained with standard physicochemical analysis. Sharp patterns are obtained with X-ray diffraction of DNA, but X-ray diffraction studies of histones provide only diffuse images in which the ring shape and the orientation of the arc are difficult to define. However, it seems well established that the DNA maintains its structure inside the nucleoprotein. Studies of nucleohistones by infrared spectroscopy or rotatory dispersion have also yielded results that are not easily interpreted. 

Nucleoproteins, in which nucleic acids combine in some manner with proteins, are found in most living cells. Modes of combination between these two groups of biopolymers appear to be of various kinds. Some are readily dissociable into their components while others are not. Examples of dissociable nucleoproteins are the nucleohistones in the nuclei of somatic cells of animals and the nucleoprotamines in the sperm cell nuclei of some fish. In these cases the nucleic acid moiety is deoxyribonucleic acid. 

Carter, R. O. The physical-chemical investigation of certain nucleoproteins. III. Molecular kinetic studies with calf thymus nucleohistone. J. Amer. chem. Soc. 63, 1960—1964 (1941). 

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