It is proposed in this research plan to study interactions between model proteins and nucleic acids. Model proteins will be synthetic copolypeptides, random or sequential, which have two types of amino acid residues, lysine (or arginine) plus one type of nonbasic amino acid residues, alanine, phenylalanine etc. Nucleic acids will be natural DNAs of varied G plus C contents, denatured DNA, synthetic DNAs, single-or double-stranded RNAs, oligonucleotides and mononucleotides. Both structures and interactions in the complexes (in protein or nucleic acid moieties) will be studied using thermal denaturation, circular dichroism (CD), nuclear magnetic resonance (NMR), light scattering, fluoresence and other methods. These investigations will reveal roles played by individual amino acid residues in proteins, nucleotide bases in nucleic acids and structures of both proteins and nucleic acids in protein-nucleic acids interactions, which play key roles in regulation of many biological processes, either at chromosomal level (gene activation and repression through the binding of histones, nonhistone proteins, hormone-receptor complexes, replication and transcription) or in cytoplasm (translation of mRNA into protein, for example). Such fundamental knowledge will add to our understanding of the causes and the controls of cell differentiation, aging, cancer, genetic diseases and hormone actions.