King, J. and Mykolajewycz, N. (1973) J Mol Biol., 75(2), 339-358.

Bacteriophage T4 tail assembly: proteins of the sheath, core and baseplate.


Structural intermediates in phage tail formation have been isolated by sucrose gradient centrifugation from cells infected with mutants blocked at various stages in tail assembly. The polypeptide chains of these structures containing 14C-labeled amino acids have been analyzed by sodium dodecly sulfate-acrylamide gel electrophoresis, enabling us to identify the proteins forming the various morphological components of the tail. Comparison of sheathed tails with core-baseplates shows that the contractile sheath is composed of a single species of subunit, the product of gene 18 (mol.wt 80,000). The site for head attachment terminating the tail is composed of the product of gene 15 (mol.wt 35,000). Comparison of core-baseplates with free baseplates shows that the tail core is composed of a single species of subunit, the product of gene 19 (mol.wt 21,000).

Free baseplates are composed of at least twelve species of proteins: the products of genes 6, 7, 8, 9, 10, 11, 12 and 29, and four genetically unidentified species.

The incomplete tails which accumulate in cells infected with mutants defective in genes 9, 11 and 12, which specify proteins on the outside of the baseplate, have also been characterized. Tails from 9- lysates lack only P9. Tails from 11- lysates lack both P11 and P12. Tails from 12- infection lack only P12. Incorporation of P12 into the baseplate requires the function of gene 57, which is also required for tail fiber assembly. P57 thus appears to take part in the maturation of three different phage structural proteins.

The sequential nature of the protein interactions in tail formation is discussed in terms of the regulation of morphogenesis at the level of assembly.

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