THE CRYSTAL-STRUCTURE OF BACTERIOPHAGE-GA AND A COMPARISON OF BACTERIOPHAGES BELONGING TO THE MAJOR GROUPS OF ESCHERICHIA-COLI LEVIVIRUSES

The three-dimensional structure of the small T=3 RNA bacteriophage GA has been determined at 3.4 Angstrom resolution. The structure was solv ed by molecular replacement, using the phage MS2 as an initial model. A comparison of the protein shells of the four related phages GA, MS2, fr and Q beta was carried out in order to define structural features of particular importance for their assembly and specific RNA interacti on. A. high degree of similarity was found in the RNA binding sites, w hereas larger structural differences are located in the loop regions o f the coat proteins, especially in the FG loops forming 5-fold and qua si-6-fold contacts. The overall arrangement of the protein subunits in the shells of these phages is very similar, although the details of: the interactions differ. The few conserved interactions are suggested to govern the subunit packing during assembly. (C) 1997 Academic Press Limited.