The herpes simplex virus DNA polymerase: analysis of the functional domains

The structural and functional organization of the herpes simplex virus type I (HSV-1) DNA polymerase enzyme of strain ANG was studied by a combination of sequence and immunobiochemical analyses. Comparison of the HSV-1 ANG DNA polymerase sequence with those of pro- and eukaryotic DNA polymerases resulted in the allocation of eleven conserved regions within the HSV-1 DNA polymerase. From the analysis of all currently identified mutations of temperature-sensitive and drug-resistant HSV-1 DNA polymerase mutants as well as from the degree of conservancy observed, it could be deduced that the amino-acid residues 597-961, comprising the homologous sequence regions IV-IX, constitute the major structural components of the catalytic domain of the enzyme which should accommodate the sites for polymerizing and 3'-to-5' exonucleolytic functions. Further insight into the structural organization was gained by the use of polyclonal antibodies responding specifically to the N-terminal, central and C-terminal polypeptide domains of the ANG polymerase. Each of the antisera was able to immunostain as well as to immunoprecipitate a viral polypeptide of 132 +/- 5 kDa that corresponded well to the molecular mass of 136 kDa predicted from the coding sequences. Enzyme-binding and neutralization studies confirmed that both functions, polymerase and 3'-to-5' exonuclease, are intimately related to each other, and revealed that, in addition to the sequences of the proposed catalytic domain, the very C-terminal sequences, except for amino-acid residues 1072-1146, are important for the catalytic functions of the enzyme, most likely effecting the binding to DNA.