| During lambda bacteriophage assembly, the gene product U (gpU) terminates tail{09}elongation and serves as an interface between the tail and head structures. Together, these two essential functions suggest that gpU is optimized for numerous protein-protein interactions. Using Nuclear Magnetic Resonance (NMR) methods, we present the structure of monomeric gpU. Upon addition of Magnesium ions (Mg(II)), gpU oligomerizes into a mixture of dimers, trimers and hexamers as a function of increasing protein concentration. The hexameric stoichiometry would complement that of it's protein partner, gene product V (gpV), and may represent the biologically active conformation of gpU. A D93A and D93N substitution within the well defined alpha/beta core motif abolishes sensitivity to Mg(II). As the gpU variants cannot complement phage lacking a functional gpU, a functional link is established between Mg(II) sensitivity in vitro and gpU function in vivo. |
