Putative functional domains of human cytomegalovirus pUL56 involved in dimerization and benzimidazole D-ribonucleoside activity.

Benzimidazole D-ribonucleosides inhibit DNA packaging during human cytomegalovirus (HCMV) replication. Although they have been shown to target pUL56 and pUL89 (the large and small subunits of the HCMV terminase, respectively) their mechanism of action is not yet fully understood. We aimed here to better understand HCMV DNA maturation and the mechanism of action of benzimidazole derivatives. The HCMV pUL56 protein was studied by sequence analysis of the HCMV UL56 gene and herpesvirus counterparts combined with primary structure analysis of the corresponding amino acid sequences. The UL56 sequence analysis of 45 HCMV strains and counterparts among herpesviruses allowed the identification of 12 conserved regions. Moreover, comparison with the product of gene 49 (gp49) of bacteriophage T4 suggested that the pUL56 zinc finger is localized close to the dimerization site of pUL56, providing a spatial organization of the catalytic site that allows recognition and cleavage of DNA. This study provides a basis to investigate the mechanism of concatemeric DNA cleavage and a biochemical basis for DNA packaging inhibition by benzimidazole derivatives.