DIRECT RECOGNITION OF THE TRP OPERATOR BY THE TRP HOLOREPRESSOR - A REVIEW

Two different X-ray co-crystal structures of the Escherichia coli trp holorepressor complexed with DNA suggest that the TrpR protein recogni zes specific DNA sequences primarily with a network of water-mediated H-bonds. However, the more recent nuclear magnetic resonance (NMR) sol ution structures of the holorepressor-operator complex show no long-li ved ordered water molecules at the protein-DNA interface and place ami no acids in intimate contact with nucleotide bases. Both genetic and b iochemical studies support a model in which the trp repressor recogniz es specific DNA sequences by a direct mechanism, as seen in the NMR so lution structures, not by the 'indirect readout' mechanism initially p roposed on the basis of X-ray studies.