The lytic cycle of phage 41c required the presence of at least 10 m-calcium. In the absence of this ion, the plaquing efficiency of the virus was reduced to less than 0.1. Likewise, replacement of Ca with other divalent ions (Ba, Sr, Mg, Mn) resulted in reduced efficiencies.

Adsorption of 41c was Ca-dependent, requiring concentrations ranging from 0.1 to 10 m. Although more than 90% of the phage adsorbed at 0.1 m-Ca, successful infection could only be achieved at higher Ca levels. Sub-optimal concentrations of the ion resulted in the loss of 90% of infected centres within 1 min after the initiation of infection, indicating an early post-adsorption ion requirement. Penetration experiments with P-labelled phage DNA indicated that an irreversible inhibition of injection was occurring in the majority of the phage-bacterium complexes. A third level of cation involvement became apparent when phage-bacterium complexes in which penetration had occurred exhibited a greatly reduced burst size. The post-penetration ionic requirement occurred early in the infection process since dilution of infected complexes into Ca-free medium at 2.5 min p.i. resulted in reduced phage yields. The requirement was dispensable after 6 min p.i., since infected complexes diluted into Ca-free medium at this time exhibited a normal one-step growth curve. Analysis of messenger RNA production by molecular DNA-RNA hybridization techniques indicated that transcriptional events were similar in the presence and absence of Ca. At present, the identification of the third ion-dependent stage is unresolved.


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