Studies on the structure, protein composition and aseembly of the neck of bacteriophage T4

We have developed an osmotic shock procedure which disconnects the tail from the head of intact bacteriophage T4, leaving the neck region attached to the tail. Purification of these necked tails permitted detailed structural observations of the neck and the collar/whisker complex attached to it, as well as comparison by gel electrophoresis with tails lacking the neck. Five or six neck proteins were found: N1 (M_r = 52,000; 39 copies/phage) is the product of the wac³ gene (Pwac), forms both the collar and six whiskers as a multimeric fibrous protein, and probably assembles onto phage after head to tail joining; N2 (M_r= 35,000; 5 to 6 copies/phage), N3 (M_r= 33,000; 17 copies/phage) identified here as P13, and N6 (M_r= 28,000; 10 to 11 copies/phage) are all assembled in heads prior to tail joining; N4 (M_r= 32,000; 6 to 9 copies/phage) is unusual in that it is present in wac or wac⁺ phage and necked tails but is absent from purified heads; N5 (M_r =29,000) is probably P14 and like N4 is not found in heads. However, while we find one to two copies of N5 per necked tail, we have not observed it in phage.An aberrant neck structure called the extension assembles on the distal end of the tail connector late (after 33 min, 30 °C) in head-defective, mutant-infected cells. The extension contains five of the six neck proteins (N2 is absent), and blocks head to tail joining in vitro. Mutations in genes 13 and 14, and the double mutant 49:Wac block extension assembly.Other results show that the wac mutant E727J is an amber lesion, and that Pwac can assemble on collarless, wac phage in vitro.