A number of different microbial pathogens code for their own enzymes involved in the synthesis of a cap structure [5, 6, 7, 8, 9, 10] . Although the RNA cap structures originating from human and microbial enzymes are often identical, the physical organization of the genes, subunit composition, structure and catalytic mechanisms of the microbial-encoded enzymes involved in the synthesis of the RNA cap structure are often significantly different from those of host cells [2] . As a consequence these pathogenic capforming enzymes are potential targets for anti-microbial drugs.