[Thermic melting and optical rotatory dispersion of DNA-Hg2+ complexes]

Fine structure in the thermal denaturation of DNA: high temperature-resolution spectrophotometric studies

Fine structures which appear in the optical melting profile of DNA are examined from both the experimental and theoretical aspects. After a brief historical survey of the DNA melting experiments during the pre-fine-structure era in Section II, the high temperature-resolution experimental techniques which are essential to the investigation of fine structure are described in Section III. Then, the current status of the high-resolution study is reviewed first by a phenomenological description of the melting profile (Section IV) and then of the refolding profile (Section V), where a general idea about the cooperatively melting region and several factors affecting it is given. Sections VI and VII are devoted to the review of current theoretical works. Several well-established theoretical frameworks which correlate the base sequence with the melting phenomena are examined in terms of their rigorousness and usefulness. The molecular thermodynamic parameters concerning the DNA melting which have been evaluated by several research groups are compared and discussed. Finally, in Section VIII, current ideas on the correlation between the fine structure and genetic functions and genetic maps are reviewed. Some future problems relating to the fine structure are also discussed.

Interactions of Hg(II) ions with DNA as revealed by CD measurements

The circular dichroism spectra of Hg(II) complexes with native calf thymus DNA, chemically methylated Streptomyces chrysomallus DNA and with Ag(I)-DNA complexes were measured in the region of 220 - 340 nm. As a main result a conversion of the conservative CD spectrum of DNA to a distinct nonconservative type of CD spectrum for the complexes occurs with increasing Hg(II) concentration. The CD spectra of the Hg(II) complexes as well as some additional arguments strongly support the idea, that DNA in the complex undergoes a structural transition to a more condensed state with 4 -like character.