STRUCTURE, INTERACTIONS AND DYNAMICS OF PRD1 VIRUS .2. ORGANIZATION OF THE VIRAL MEMBRANE AND DNA

Structure, dynamics and stability of the membrane and double-stranded (ds) DNA genome packaged within the native PRD1 virion have been probe d by laser Raman spectroscopy. The Raman signature of PRD1 is complex, but exhibits distinctive marker bands diagnostic of the internal lipi d bilayer and dsDNA. The Raman markers demonstrate, respectively, a li quid crystalline lipid phase (L(alpha)) and a B DNA conformation throu ghout the temperature range (5 degrees C to 50 degrees C) of virion st ability. Despite the absence of large scale lipid phase transitions or DNA melting, small temperature-dependent changes in the Raman markers of lipid and DNA are detected, indicating coupling between their stru ctures. Minor deviations of DNA from the canonical B form are imposed by the membrane. The Raman markers indicate further that base stacking and phosphate group interactions of the packaged PRD1 genome differ f rom those of unpackaged PRD1 DNA. Specific Raman band perturbations ar e proposed as indicators of DNA-membrane interaction. Hydrogen-deuteri um exchange kinetics of packaged and unpackaged PRD1 DNA are indisting uishable, demonstrating that base imino and amino protons are not affe cted significantly by either the condensation or membrane enclosure as sociated with DNA packaging. This contrasts with the significant accel eration of base exchanges detected in the packaged DNA of bacteriophag e P22, which lacks a viral membrane. The distinctive H-->H-2 exchange profile of the PRD1 genome, the absence of packaging-induced accelerat ion of exchange kinetics and the apparent direct interaction between D NA and phospholipids suggest a specific role for the viral membrane in PADI assembly We propose a ''membrane-surface-catalyzed'' model for d sDNA condensation and organization within the PRD1 virion. (C) 1996 Ac ademic Press Limited