Adsorption and Eclipse Reactions of the Isometric Phages

Abstract

Recent advances in the sequencing of the nucleic acid and capsid proteins of ϕX174 provide an opportunity to examine in more detail the early interactions between this virus and its host. The objectives of such studies are usually twofold. First, these processes involve both the formation and disruption of noncovalent interactions between proteins, nucleic acids, and, in the case of some viral receptor sites, carbohydrates. Therefore, the adsorption and nucleic-acid-injection steps of a relatively simple virus such as ϕX can serve as a model system for elucidating the precise structural features of these interactions and the roles they play in determining the rate of these reactions in vivo. Second, an understanding of the mechanisms by which viruses deliver their genomes to host replication systems may lead to the development of antiviral agents for prevention of and therapy for viral diseases.

Adsorption
In the earliest studies (Fujimura and Kaesberg 1962) the adsorption of infectious virus to intact cells was shown to follow pseudo first-order kinetics in the presence of excess bacteria, as is the case with most phage systems. The requirement for divalent cations and pH dependence were established. The latter seems noteworthy since the rate increased dramatically between pH 6.0 and pH 7.5, suggesting that a particular class of ionizable groups on either the viral capsid proteins or the host receptor plays an important role. The values of the rate constants in the simple aqueous solvents of this study compare reasonably well with those obtained subsequently in a complex starvation...