THE ROLE OF THE ADSORPTION COMPLEX IN THE TERMINATION OF FILAMENTOUS PHAGE ASSEMBLY

The adsorption complex of filamentous phage fd consists of two minor c oat proteins, g3p and g6p, and is considered to be not only a structur al entity, but also a functional unit to terminate phage assembly. Cel ls were infected with phage M13am8H1, which cannot assemble because it lacks the major coat protein g8p, although producing ah of the other minor coat proteins. The membranes of infected cells were solubilized and analysed by non-denaturing PAGE and gel filtration. The data sugge st the presence of the adsorption complex in these membranes. Furtherm ore, the non-polar gene 3 amber-mutant phage R171 was shown to lack g6 p in the phage coat as well. The termination of assembly of this phage is disturbed, resulting in synthesis of polyphages. Electron microgra phs and transient electrical birefringence show that these polyphages are eight times longer as compared to unit length phage. From these re sults, we conclude that the formation of the g3p-g6p complex is essent ial for correct termination of filamentous phage assembly.