in vitro MORPHOGENESIS OF PHAGE P22 FROM HEADS AND BASE-PLATE PARTS.

The in vitro reconstitution of tobacco mosaic virus from its RNA and protein subunits1' 2 has presaged the in vitro assembly of structurally more complex viruses like T4,3 P22,4 and X5 bacteriophages from various component parts. Here we give a detailed report of experiments4 demonstrating the efficient in vitro assembly of P22 bacteriophage whose DNA is normally contained in a polyhedral head to which a small base plate is attached (Fig. 1A). Viewed end on, the base plate appears to consist of a central core around which are arranged six spikes.6 We have purified both the tail molecules of which these base plates are composed and noninfectious DNA-containing P22 heads that have short necks but no base plates. When the two preparations are mixed, a number of tail molecules combine at the neck to make the base plate required for infectivity. P22 particles thus made in vitro are fully active and are morphologically indistinguishable from particles that have been assembled in vivo.