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

Abstract

The in vitro assembly does not appear to require the intervention of an enzyme, for it is extremely efficient when purified head and tail-part preparations are mixed. The firm bonds that hold P22 tail parts to the head apparently do not involve disulfide bonds. They could well be similar to the specific polar, hydrophobic, and cooperative interactions which hold antigens and antibodies together, but the effects of salt concentration seem to be unusual. The initial lag in the formation of infectious particles after heads and tail parts are mixed shows that the assembly of P22 (like the addition of tail fibers to T43 but unlike the addition of tails to [lambda] 5) is a multistep reaction that involves the successive addition of a number of tail parts. The number of tail parts proved surprisingly difficult to derive without ambiguity. Both the electron microscopic observations and the determinations of molecular weights suggest that 6 tail parts are required to make a complete base plate, but the stoichiometric experiments suggest that as few as 3 may suffice for infectivity. The possibility exists that incomplete base plates, with as few as 3 tail parts, may confer infectivity on some of the heads to which they are attached.