Bacteriophage lambda preconnectors. Purification and structure |
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Authors: | J Kochan J L Carrascosa H Murialdo |
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Affiliation: | 1. Department of Medical Genetics, Medical Sciences Building University of Toronto, Toronto, Ontario M5S 1A8 Canada;2. Centro de Biologia Molecular, Facultald de Ciencias Universidad Autonoma, Canto Blanco Madrid-34 Spain |
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Abstract: | The morphogenesis of bacteriophage lambda proheads is under the control of the four phage genes B, C, Nu3 and E, and the two Escherichia coli genes groEL and groES . It has been shown previously that extracts prepared from cells infected with a lambda C-E- mutant accumulate a gpB polymer, which behaves as a biologically active intermediate in prohead assembly. This gpB activity has been called a preconnector , as it is probably a precursor to the head-tail connector. We now report the partial purification of biologically active preconnectors and the characterization of its structure. In the electron microscope, preconnectors appear as donut -like structures composed of several subunits displaying radial symmetry. Optical filtration of periodic arrays of preconnectors showed that the structure has 12-fold rotational symmetry. Side views of the preconnector reveal that it resembles an asymmetrical dumbell . This information has been used to construct a three-dimensional model of the preconnector . The implications of this structure for prohead shape and function, and for DNA packaging are discussed. |
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