STRUCTURAL STUDIES OF PROTEIN-NUCLEIC ACID INTERACTIONS.

Recently the structures of three proteins that regulate gene expression have been determined: the Cro repressor protein from bacteriophage lambda , the cI or lambda repressor protein, also from phage lambda , and the catabolite gene activator protein from Escherichia coli. Each of these proteins binds specifically to sites on double-stranded DNA that are distinguished by the sequence of base pairs within the binding region. Knowledge of these structures has thrown new light on many of the important aspects of gene regulation, and this paper reviews recent progress in this area. It discusses structural studies of Cro, CAP, and cI which suggest a number of general principles for DNA-protein recognition and for positive and negative regulation of gene expression, including symmetry, alpha-helical fold, sequence-specific recognition, flexibility, DNA confirmation, negative and positive gene regulation.