Kikuchi, Y and King, J. (1975) J Mol Biol., 99(4) 673-694

Genetic control of bacteriophage T4 baseplate morphogenesis.
II. Mutants unable to form the central part of the baseplate


The products of the group II baseplate genes, 5, 25, 25 ,51 ,27, 28 and 29, are needed for baseplate morphogenesis, but make only a small contribution to the total protein composition of the baseplate. To understand the function of these gene products we have examined the state of the major baseplate structural proteins in cells infected with amber mutants defective in the group II genes. These infected cells accumulate normal 15 S arm complexes and small amounts of organized 70 S structures. Electron microscopic examination of the 70 S material reveals unstable sixfold-symmetric structures lacking the central hub of the baseplate.

The protein compositions of the 70 S structures from all the mutant lysates were similar and showed clearly that the 70 S stuctures were polymerization products of the 15 S precursor, representing either aberrant aggregates or unstable intermediates. In the course of these analyses five more baseplate proteins were identified as the products of known phage genes: gene 5 protein, 44,000 daltons; gene 53 protein, 23,000 daltons; gene 25 protein, 15,000 daltons; gene 48 protein, 44,000 daltons; and gene 54 protein, 36,000 daltons. Only one baseplate protein, designated pY (22,000 daltons) remains unidentified genetically. 18 of the 19 phage tail proteins resolved on sodium dodecyl sulfate acrylamide gels have now been identified with the genes coding for them.

The baseplate-like structures from all the group II mutant lysates lacked the same five minor baseplate proteins (gp5, gp29, gp54, pX and pY). This suggests that these proteins and the other group II gene products interact with each other in a common pathway. The electron microscopy results suggest that the end-product of this pathtway is the central plug of the baseplate.

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