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Published June 28, 1969 | public
Journal Article

The process of infection with bacteriophage φX174: XXVII. Removal of the Spike Proteins from the Phage Capsid

Abstract

Electron microscopy of negatively stained bacteriophage φX174 has revealed a set of projections or "spikes" which protrude from the 12 vertices of the icosahedral virus particle. Urea treatment can remove these spikes, leaving an intact protein shell or capsid. Capsids produced by this procedure are readily separated from the smaller spike material by sedimentation in a sucrose gradient. Electrophoresis of dissociated phage proteins in polyacrylamide gel has shown that the φX particle contains most probably four different proteins. Only one of these is present in purified capsids prepared by the above procedure. The slow-sedimenting spike material contains the other proteins. The amino acid composition and fingerprints of the capsid and spike proteins are presented. A model of the structure of the phage particle, based on these studies of the phage proteins and electron micrographs of intact phage and spikeless capsids, is proposed. This model consists of a modified Caspar-Klug capsid in which the 12 pentamers located at the vertices of the icosahedral structure are replaced by the structurally complex spikes. Removal of the spike proteins leaves a coat structure composed solely of hexamers of a single molecular species.

Additional Information

© 1969 Elsevier Ltd. Received 31 December 1968, Revised 14 March 1969. We acknowledge W.R. Gray, L. E. Hood and W. J. Dreyer, who introduced us to the techniques of protein chemistry. We thank J. Raes for performing the amino acid analyses. We also thank J.E. Newbold for tho gift of various radioactively labelled ϕX preparations. This work was supported in part by a grant GM-13554 from the U.S. Public Health Service.

Additional details

Created:
August 19, 2023
Modified:
October 18, 2023