Structure of Ribonuclease H Phased at 2 Å Resolution by MAD Analysis of the Selenomethionyl Protein

Ribonuclease H digests the RNA strand of duplex RNA⋅DNA hybrids into oligonucleotides. This activity is indispensable for retroviral infection and is involved in bacterial replication. The ribonuclease H from Escherichia coli is homologous with the retroviral proteins. The crystal structure of the E. coli enzyme reveals a distinctive α-β tertiary fold. Analysis of the molecular model implicates a carboxyl triad in the catalytic mechanism and suggests a likely mode for the binding of RNA⋅DNA substrates. The structure was determined by the method of multiwavelength anomalous diffraction (MAD) with the use of synchrotron data from a crystal of the recombinant selenomethionyl protein.