Ultraviolet absorption and optical rotatory dispersion studies of deoxyribonucleic acid and nucleohistone.

This report concerns the ultraviolet absorption and optical rotatory dispersion (ORD) of DNA and of nucleotides down to 185 mp. An absorption band (y) at about 195 mp occurs for all these compounds. Similar studies have been made on histones and nucleohistone. These indicate a strong absorption below 200 mp due to protein. Consequently, if any native DNA is associated with some amount (2 — 12%) of protein (e.g., histones), the molecular absorption of DNA in the said region becomes masked, and no clear y-maximum due to DNA occurs in the absorption spectrum. The absorption of DNA in the y-band region (ca. 190 m^a) seems to be decreased as a result of DNAprotein interaction. No significant change is observed in the absorption region of DNA at longer wavelengths (250 — 290 m^)The y-peak of DNA appears at about 190 m/i on complete removal of proteins. This peak is sharper than the conventional one (x) at 260 mp and is hyperchromic on denaturation, and involves multiple C o t t o n effects to any degrees similar to that observed at the second peak (260 m « ) . The absorption (also ORD) features of nucleohistone at the x and y wavelengths do not provide similar information (e. g., denaturation artefacts) regarding the structure of the nucleohistone contained DNA which is apparently distinct from the structures of native and partially denatured (denaturation 10%) DNA. The weaker n—:i* transition (190 m/c) in the DNA bases is very susceptible to nucleoprotein interaction. This result has been used to explain the influence of nucleoprotein interaction on the configuration of DNA in nucleohistone.