AN IMMUNOBLOT ASSAY REVEALS THAT BACTERIOPHAGE-T4 THYMIDYLATE SYNTHASE AND DIHYDROFOLATE-REDUCTASE ARE NOT VIRION PROTEINS

Numerous reports describe the phage T4 enzymes thymidylate synthase an d dihydrofolate reductase as structural components of the baseplate. H owever, Y. Wang and C.K. Mathews (J. Virol. 63:4736-4743, 1989) report ed that antisera against the respective recombinant enzymes failed to neutralize phage infectivity, in contrast to previous results. Moreove r, a deletion mutant lacking the genes for these two enzymes adsorbed normally to host cells. Since these findings tended to undermine the i dea of the two enzymes as structural proteins, we developed a quantita tive immunoblot assay to resolve the issue directly. Our results show that both enzymes are present only as minor contaminants (<0.05 copy p er phage) and as such cannot be bona fide structural proteins.