title: Mechanism of coliphage M13 contraction: intermediate structures trapped at low temperatures.
abstract: The filamentous coliphage M13 can be transformed into a spherical particle (termed spheroid) by exposure to an interface of water and slightly polar but hydrophobic solvent such as chloroform-water at 24 degrees C. We report here that exposure of M13 filaments to a chloroform-water interface at 2 degrees C trapped the phage particles in forms morphologically intermediate to filaments and spheroids. These structures were rods 250 nm long and 15 nm wide, and each had a closed, slightly pointed end, an open flaired end, and a hollow central channel. The final contraction of these intermediates (termed I-forms) into spheroids was dependent upon both temperature and the presence of the solvent-water interface but was apparently independent of both the minor phage coat proteins and the virion DNA. Although stable in an aqueous environment, I-forms, in contrast to filaments, were readily disrupted by detergents, suggesting that the phage structure had been altered to a form more easily solubilized by membrane lipids. These solvent-induced changes might be related to the initial steps of phage penetration in vivo.
mesh_terms: D002725:Chloroform; D003080:Cold Temperature; D003090:Coliphages / Q000502:physiology / Q000648:ultrastructure*; D004279:DNA, Viral / Q000502:physiology; D009690:Nucleic Acid Conformation; D014764:Viral Proteins / Q000502:physiology; D014771:Virion / Q000648:ultrastructure
chemical_list: D004279:DNA, Viral; D014764:Viral Proteins; D002725:Chloroform