CRYSTAL-STRUCTURE OF BACTERIOPHAGE-T7 RNA-POLYMERASE AT 3.3-ANGSTROM RESOLUTION

The crystal structure of T7 RNA polymerase reveals a molecule organize d around a cleft that can accommodate a double-stranded DNA template. A portion (approximately 45%) of the molecule displays extensive struc tural homology to the polymerase domain of Klenow fragment and more li mited homology to the human immunodeficiency virus HIV-1 reverse trans criptase. A comparison of the structures and sequences of these polyme rases identifies structural elements that may be responsible for discr iminating between ribonucleotide and deoxyribonucleotide substrates, a nd RNA and DNA templates. The relative locations of the catalytic site and a specific promoter recognition residue allow the orientation of the polymerase on the template to be defined.