Structural analysis of the bacteriophage T3 head-to-tail connector

The connector protein of bacteriophage T3, p8, has been overexpressed in Es cherichia coli, Purification of the oligomers built by several copies of p8 reveals a mixed population of dodecamers and tridecamers. The percentages of these two types of oligomers differ in every culture growth, indicating that assembly of this protein depends upon the conditions of the expression system. Those cultures that generated a majority of dodecamers allowed, af ter purification of the connectors, the two-dimensional crystallization of the dodecamers in a tetragonal arrangement, while the tridecamers did not f orm crystals. The processing and averaging of several images of frozen-hydr ated crystals and their internal phase comparison shows that the crystals a re arranged in a P42(1)2 space group, with cell unit dimensions of 165 x 16 5 Angstrom. The three-dimensional reconstruction generated with images of c rystals ranging from 0 degrees to 60 degrees tilt reveals a wide domain sur rounded by 12 protrusions and a narrow domain that serves to interact with the tail of the bacteriophage. A channel runs along the connector wide enou gh to allow the translocation of a double-stranded DNA molecule into the pr ohead, The general structure of the T3 connector is very similar to those o btained for other nonrelated bacteriophages and strongly suggests that the shape of this important viral structure is intimately related to its functi on. (C) 2000 Academic Press.