DNA'Protein Interactions

The study of protein-nucleic acid interactions is currently one of the most rapidly growing areas of molecular biology. DNA binding proteins are at the very heart of the regulation and control of gene expression, replication, and recombination: Enzymes that recognize and either modify or cleave specific DNA sequences are equally important to the cell. Some of the techniques reported in this volume can be used to identify previously unknown DNA binding proteins from crude cell extracts. Virtually all are capable of giving direct information on the molecular basis of the interactionthe location of the DNA binding site; the strength and specificity of binding; the identities of individual groups on specific bases involved in binding; the specific amino acid residues of the protein that interact with the DNA; or the effects of protein binding on gross conformation and local structure of DNA. The recognition of DNA sequences by proteins is a complex phenomenon, involving specific hydrogen bonding contacts to the DNA bases ("direct readout") and/or interactions with the sugar-phos phate backbone ("indirect readout"). The latter interactions can also be highly specific because of sequence-dependent conformational changes in the DNA. In addition, intercalation of planar aromatic amino acid side-chains between the DNA bases can occur, most notably with single-stranded DNA binding proteins. Furthermore, when bound, many DNA binding proteins induce drastic structural changes in the DNA as an integral part of their function.